ATT Volume 12 Issue 5

ASTRONOMY

TECHNOLOGY TODAY Your Complete Guide to Astronomical Equipment IMAGING COMET 21P/GIACOBINI-ZINNER • HUBBLE OPTICS UL18F/4.5 DOBSONIAN ADVENTURES IN ASTROPHOTOGRAPHY WITH SKYTOOLS 4 IMAGING THE GODWANA TELESCOES MARANA THE 16-INCH F/4.5 COLLAPSIBLE TRUSS DOBSONIAN FROM NEW MOON TELESCOPES

EXPLORE SCIENTIFIC 68° AND 82° EYEPIECES RUGGED, WATERPROOF AND HIGH PERFORMING!

Volume 12 • Issue 5 $6.00 US

Contents

Cover Story: Pages 39-42 Our cover features Explore Scientifics’ 68° and 82° eyepieces which are reviewed in this issue by Dr. James Dire.

The background M15 astro image was taken by Greg Crinklaw as a demonstration of using Skytools 4.

In This Issue 8

GUEST EDITORIAL An ATM Exit Pupil Gauge

by Barry Simon

39 EXPLORE SCIENTIFIC 68° AND 82° EYEPIECES Why I Like These Great Eyepieces!

by Dr. James R. Dire 50 COMET 21P/ GIACOBINI-ZINNER Imaging a Visit from Afar

by Matt Harmston

ASTRONOMY

TECHNOLOGY TODAY

Industry News/New Products 10 REVOLUTION IMAGER Fine Finger Feather Focuser

Your Complete Guide to Astronomical Equipment IMAGING COMET 21P/GIACOBINI-ZINNER • HUBBLE OPTICS UL18F/4.5 DOBSONIAN ADVENTURES IN ASTROPHOTOGRAPHY WITH SKYTOOLS 4 IMAGING THE GODWANA TELESCOES MARANA THE 16-INCH F/4.5 COLLAPSIBLE TRUSS DOBSONIAN FROM NEW MOON TELESCOPES

EXPLORE SCIENTIFIC 68° AND 82° EYEPIECES RUGGED, WATERPROOF AND HIGH PERFORMING!

In This Issue

10 ASTRONOMIK New Clip Filters for Sony and Nikon Cameras

Volume 12 • Issue 5 $6.00 US

55 ADVENTURES IN ASTROPHOTOGRAPHY Imaging with Skytools 4

by Greg Crinklaw 62 THE 16-INCH F/4.5 COLLAPSIBLE TRUSS DOBSONIAN FROM NEW MOON TELESCOPES New Design Approaches and Old-Fashioned Craftmanship

by Damian G. Allis, Ph.D. 68 THE GONDWANA TELESCOPES MARANA A Big-Aperture Cure for Fat Lips and Slip Discs

by Sean Melehan

12 ZWO New Special Edition ASI128MC Pro Color IMX128 Camera

14 PRECISE PARTS Offers Updated Functionality to Its Build-An-Adapter Platform

16 FARPOINT ASTRO New JMI Hard Shell Carrying Case for Celestron AVX Mounts

Astronomy TECHNOLOGY TODAY

3

Contributing Writers Damian G. Allis is a Research Fellow with the Forensic and National Security Sciences Institute and Research Professor of Chemistry at Syracuse University. Dr. Allis’ astronomical activities include serving as president and webmaster of the Syracuse Astronomical Society, executive directorship of CNY Observers & Observing, and membership in several local observing clubs in Central New York. He lectures on topics of astronomy and space science at local libraries and state parks and coordinates with Syracuse’s Museum of Science and Technology on solar observing sessions and NASA-related events.

Greg Crinklaw operates Skyhound and is the developer of SkyTools.

He is a life-long amateur astronomer, who is also trained as a professional astronomer, holding a BS, MS in astronomy, and an MS in astrophysics. He also worked for NASA as a Software Engineer on a Mars orbital mission. Greg and his family live in the mountains of Cloudcroft, New Mexico.

James Dire has an M.S. degree in physics from the University of Central Florida and M.A. and Ph.D. degrees from The Johns Hopkins University, both in planetary science. He has been a professor of physics astronomy at several colleges and universities. He is the president of Methodist College in Peoria, Illinois. He has played a key role in several observatory projects including the Powell Observatory in Louisburg, KS, which houses a 30-inch (0.75-m) Newtonian; the Naval Academy observatory with an 8-inch (0.20-m) Alvin Clark refractor; and he built the Coast Guard Academy Astronomical Observatory in Stonington, CT, which houses a 20-inch (0.51-m) Ritchey Chrétien Cassegrain.

Matt Harmston is an educational researcher whose appetite for the heavens has been whetted by increasing aperture over the years.

More recently, Matt has immersed himself in video astronomy - a means of probing deeper into the night sky while making astronomy accessible to all ages and abilities. With this technology readily available, Matt is considering a career as a sleep-deprivation research subject.Ritchey Chrétien Cassegrain.

Contents

Industry News/New Products

18 IP4AP Warren Keller and Ron Brecher to Host PixInsight Workshop in Dallas, Texas

20 CLEARLINE TECHNOLOGY CORPORATION New Boot-Up Emulator for the Meade LX200 Hand Controller

22 SOUTHERN CROSS ASTRONOMICAL SOCIETY OF MIAMI 2019 Winter Star Party

24 10MICRON New Line of AZ-HPS Series of Mounts

Sean Melehan is an amateur astronomer who lives on Lake Macquarie, NSW, Australia, with his wife Sarah-Kate and daughter Savannah-Rose. Deep sky observing is Sean’s burning interest, and he loves nothing better than to sketch at the eyepiece.

Barry Simon lives in New Orleans and is a longtime member and former officer of Pontchartrain Astronomy Society and founder of the Deep South Regional StarGaze. His special interests include binocular astronomy and refractor repair and refurbishment.

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Astronomy TECHNOLOGY TODAY

34 SOUTHERN SKIES Releases New Version of iOS App for Tracking Satellitesp

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I Each scope offers high quality Poro Prisms. The optics are fully broadband multi-coated throughout for maximum light transmission and contrast.

I Included are a precision 4:1 ratio dual-speed focuser for exceptional focusing accuracy. The supplied 7.5-22.5mm zoom eyepiece, constructed from 8-lens elements, provides a generous 20-18mm of eye relief.

I The stylish spotting scope body is constructed from robust but lightweight magnesium alloy, with a sliding dewshield/sun shade. Fully waterproof and nitrogen-filled for clear, fog-free viewing.

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The Supporting

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We wish to thank our advertisers without whom this magazine would not be possible.

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ASTRONOMY

TECHNOLOGY TODAY

Volume 12 • Issue 5 Publisher Stuart Parkerson

Managing Editor Emeritus Gary Parkerson

Associate Editors

Guest Editorial Barry Simon

Austin Grant Sean Melehan Chad E. Patterson

AN ATM EXIT PUPIL GAUGE

Logan Parkerson

Art Director Lance Palmer

Web Master Bandwise

3825 Gilbert Drive Shreveport, Louisiana 71104 info@astronomytechnologytoday.com www.astronomytechnologytoday.com Astronomy Technology Today is published bi-monthly

by Parkerson Publishing, LLC. Bulk rate postage paid at Dallas, Texas, and additional mailing offices. ©2012 Parkerson Publishing, LLC, all rights reserved. No part of this publication or its Web site may be reproduced without written permission of Parkerson Publishing, LLC. Astronomy Technology Today assumes no responsibility for the content of the articles, advertisements, or messages reproduced therein, and makes no representation or warranty whatsoever as to the completeness, accuracy, currency, or adequacy of any facts, views, opinions, statements, and recommendations it reproduces. Reference to any product, process, publication, or service of any third party by trade name, trademark, manufacturer, or otherwise does not constitute or imply the endorsement or recommendation of Astronomy Technology Today. The publication welcomes and encourages contributions; however is not responsible for the return of manuscripts and photographs. The publication, at the sole discretion of the publisher, reserves the right to accept or reject any advertising or contributions. For more information contact the publisher at Astronomy Technology Today, 3825 Gilbert Drive, Shreveport, Louisiana 71104, or e-mail at info@astronomytechnologytoday.com.

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Astronomy TECHNOLOGY TODAY

As we close out 2018, we want to give everyone our wishes for a happy holiday and an amazing new year! And, as we end this year and internally discuss different ways in the future of using this space in the magazine, we thought we would bring back an interesting contribution originally sent to us by Barry Simon in 2009. We hope you enjoy!

Measurement of the dark-adapted exit pupil has been a discussion point for years, with various devices having been tried to facilitate measurement under dark skies (or maybe not so dark skies).

One of the better and easies methods has been use of Allen wrenches of varying diameter held close to the pupil with the diameter of the smallest wrench that totally occults a bright star

representing a rough estimate of that of the dark adapted pupil. If you can see the star using the next smaller diameter, your pupil diameter is somewhere between the two. Of course, Allen wrenches are 6-sided, so diameter varies slightly depending on how it is oriented.

I’ve incorporated the basic Allen wrench technique into an easy to make and to use Exit Pupil Gauge (EPG), using various diameters of aluminum tubing readily available from hobby shops. I use tubing diameters of 9/32 inch (7.14 mm), 1/4 inch (6.36 mm), 7/32 inch (5.56 mm), 3/16 inch (4.72 mm), 5/32 inch (3.97 mm), 1/8 inch (3.18 mm), 3/32 inch (2.38 mm), and 1/16 inch (1.59 mm). Each section of tubing will slide fairly tightly into the

next larger size.

I cut 1-inch lengths from each tube and fit one into the other as shown in the accompanying photo of an assembled EPG that’s ready for painting. It has a finished total length of approximately 5 inches. The second through seventh tube sections each extend 5/8 inch (16 mm) from the larger section into which they are fitted. I fastened the seven tube sections with JB Weld, an epoxy like adhesive.

After completing an EPG, I prime it and apply a finish coat of Krylon Semi-Flat Black enamel to minimize reflections. After painting, the seven sections have final diameters of: 2.4 mm, 3.2 mm, 4.0 mm, 4.8 mm, 5.6 mm, 6.4 mm, and 7.2 mm.

Using the EPG To use the EPG under dark skies, locate a bright star (preferably Mag. 1 or 2) and hold the EPG by the narrow end close to or against the cheek below the eye you are testing. The upper end will likely be on or above your eyebrow with either the third (5.6-mm) or fourth (4.8-mm) section at eye level. Close your other eye and roll the EPG left or right in an effort to block the light of the target star.

If you can still see the star despite rolling the tube section in front of your eye pupil, your pupil is larger than the diameter of that section of the EPG. Pull the EPG down to align the next larger tube section, roll it, and repeat until a section completely blocks the star. Your pupil diameter falls somewhere between the diameter of that tube section and that of the next smaller tube section.

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NEWPRODUCTS/INDUSTRYNEWS

REVOLUTION IMAGER Fine Finger Feather Focuser Yes, you read that right, it’s a Fine Finger Feather Focuser. At ATT, we love a cool, handy new product. And if you add alliteration to it, we are all in!

All kidding aside, the team at Revolution Imager has come up with a nifty tool that provides an easy and more accurate way to focus your Celestron or Meade Maksutov and Cassegrain telescopes. Simply press the Fine Finger Feather Focuser lever on your SCT or Mak focusing knob to give you an even smoother feel than what you are accustomed to as well as making it easier to precisely focus.

When not in use, the lever has a built in 1.25" Dust Cover cap to store at the back of the telescope or in your eyepiece tray when not in use - another handy little feature.

The tool comes in three sizes: Celestron Regular which fits their 4" Mak, 5", 6",8" and 9.25" SCT; Celestron Large which fits their 11" and 14" SCT; and Meade SCT which fits their SCT telescopes.

The Fine Finger Feather Focuser is priced at $19.99 - inexpensive enough to buy one for yourself and one for an observing buddy.

And as the Revolution Imager team says on their website, "Give me a lever and I will move the world, or find tack sharp focus on nebula" - Archimedes (...well if he was into Astrophotography he would have said it!).

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ASTRONOMIK New Clip Filters for Sony and Nikon Cameras

Astronomik now is offering its popular Clip-Filters for Sony and Nikon cameras. Astronomik’s Clip-Filter offerings are hugely popular with DSLR camera owners for astro imaging. Ingenious in their design, these custom-made filters fit inside

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Astronomy TECHNOLOGY TODAY

the housing of the camera, just behind the lens or T-ring. No tools are necessary to use them, as they just pop in and out.

According to Gerd Neuman with Astronomik, “After a long period of prototyping and development we are now

able to offer Clip-Filters for Sony Alpha bodies and XL-Clip Filters for Nikon bodies. The filters are held in place safe and secure with no stress to the highquality glass.”

The Sony Clip-Filters are designed and optimized to be used with normal lenses and with telescopes as well. The Clip-Filters have been successfully tested with all Sony Alpha 7 bodies (7, 7r and 7s in Mk I, MkII and Mk III versions) and the Sony Alpha 9 body.

For Nikon enthusiasts, Astronomik now offers XL-Clip Filters for the full format bodies from Nikon. Neuman reports that due to the very tight Nikon bajonet, the clip-filters add a minimal obstruction at the edge of the field.

The Nikon XL-Clip Filter have been successfully tested with the Nikon D800, D810 and the D850 models (other bodies have not been tested yet). The Nikon XLClip will not work with cameras with APS-C sized sensors nor with the new mirrorless body. Neuman says that ClipFilters for the APS-C sized models will be released in the near future.

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ZWO New Special Edition ASI128MC Pro Color IMX128 Camera The special edition single-shot color ZWO ASI128MC Pro camera is ZWO’s first full-frame color astronomy camera.

It utilizes a full-frame 24 megapixel CMOS Sony sensor with TEC-cooling.

The ZWO ASI128MC-Pro camera features the full-frame Sony IMX128 CMOS sensor with 6032x4032 resolution, 5.97-micron pixel size, 76000e full well capacity, and peak QE of 53%. The 36mmx24mm sensor provides the ability to capture detailed, low-noise, and extremely sharp color images of deep-sky objects such as diffuse nebulae, supernova remnants, and large galaxies and galaxy clusters. The IMX128 CMOS

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Astronomy TECHNOLOGY TODAY

The camera has a diameter of 86mm and weighs 640 grams. It comes with a padded carrying bag, M42-M48 adapter, M54-M48 21mm extender and M48M48 16.5mm extender, 2” cover, USB3.0 and USB2.0 cables, and a quickstart guide.

FEATURES INCLUDE:

sensor offers a new level of performance in high image resolution and quantum efficiency, lower read noise, and faster image transfer rates.

The ‘Pro’ designation of the camera comes from its internal 256MB DDR3 buffer for quick and stable data transfer and reduced amp glow. The USB3.0 port offers a fast 7 fps capture rate at full resolution with 14-bit ADC and 2.5e read noise. The TEC cooling system brings the sensor temperature down to 35oC below ambient to keep sensor noise as low as possible, even on warm nights.

The camera incorporates a 6W dew heater to keep its AR-coated window free of moisture during imaging runs.

You can switch the heater off with the camera control software to save power on nights when the humidity is low.

The camera also includes a unique tilt adapter to reduce issues related to the tilt angle of the front of camera.

The camera draws 650mA@5V, more than cameras with smaller sensors, but it can still draw all the power it needs from its main USB3.0 port. The camera’s TEC cooler requires 12V@3A provided with an external power supply (not included). If the camera is powered with a USB2.0 host, the external 12V power supply is also required. The ASI128 incorporates a USB2.0 hub for powering accessories such as a guide camera and electronic focuser.

• DDR Memory Buffer includes one 256MB DDR3 memory buffer for data transfer stability • Low read noise, high dynamic range, 53% peak QE and AR protection window are major advantages of the ASI128 Pro • The IMX128 has a higher resolution, QE and lower read noise and faster FPS than old full frame CCDs • Unique tilt adapter included • 2 stage TEC cooling system included to allow up to -35°C below ambient cooling (an external power supply is needed) • Anti dew heater for heat power at 6W to prevent dew. Can be turned off via software • 5Gb bandwidth provided by USB 3.0 port allows the ASI128 Pro to run at 7fps (14 bit) or 10 fps (10 bit high speed) at 24mp resolution • USB 3.0 provides 1000mA current meaning an external power supply isn't needed to run camera • External 12v power supply needed if connecting camera with USB 2.0 host (500ma provided), or 3A or more DC adapter for cooler power supply is suggested • Battery from 9-15V is also suitable for cooler power supply • Filter wheel, guide camera and electronic focuser can be connected with USB 2.0 hub.

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NEWPRODUCTS/INDUSTRYNEWS

PRECISE PARTS Offers Updated Functionality to Its Build-An-Adapter Platform In the Looking Back section of the last issue of ATT, we featured Craig Stark’s article that demonstrated how PreciseParts is your machinist in the cloud.

For those of you that are not familiar with PreciseParts, owner Ashley Stevens started the company in 2002 in Miami. They specialize in making precision custom adapters and one-of-a-kind telescope accessories. With their online Build-An-Adapter platform, almost any custom adapter can be designed and ordered online in just a few clicks or taps.

They are experts in making high quality custom adapters with fast turnaround for astronomy and astrophotography although they also occasionally make parts for other fields. All of their products are custom CNC machined, one at a time. They do not carry off-the shelf inventory.

PreciseParts now ships to more than 2,000 customers in 47 countries on 5 continents, and they count among their clients some of the top astro-photogra-

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Astronomy TECHNOLOGY TODAY

phers in the world.

Ashley reached out to let us know he has made a number of updates to the Build-An-Adapter platform to make the experience even easier and intuitive than it was before. These updates include: • The user interface has been redesigned for a streamlined experience and now includes a rolling banner providing a quick “how-to” guide to design an adapter.

• The site now uses Secure Socket Layer (e.g. HTTPS) for user privacy and security.

• The user interface adapts automatically to screen size, optimizing experience whether the user is on a desktop or a smartphone.

• PreciseParts now uses WebGL to render a created part in virtual reality. This makes the 3-D animations extremely realistic as a part can be rotated and zoomed with clicks or touch. WebGL is supported with all recent web browsers, both desktop and mobile.

• The new Order Status page provides

a quick way to check the progress of an order with no need to supply personal information.

• They now offer a Spanish and Simple Chinese language version of the platform in addition to English.

• The Help section has been greatly expanded based on users’ feedback and there is also a Search field at the top of every page to quickly find an answer in the FAQs section, or to locate a particular device in the database.

NEWPRODUCTS/INDUSTRYNEWS

FARPOINT ASTRO New JMI Hard Shell Carrying Case for Celestron AVX Mounts For over 35 years, Jim Burr and JMI Telescopes created novel products for the telescope industry. Innovations included Wheely Bars, the Motofocus, and others which became household names to the amateur astronomy community.

When Jim was ready to release the reigns of the business, Farpoint Astro stepped in and now carries over 180 JMI products, ensuring that JMI’s legacy will continue far into the future.

One of the products JMI has been well known for are its line of hard-shell carrying cases. These cases are designed to perform for decades, safely cradling well loved telescopes and accessories. Farpoint continues to expand the JMI carrying case options and has introduced the JMI hard shell carrying case for the Celestron AVX mount head and components.

The case is available in two options which include a Standard carrying model and a Deluxe model which includes wheels and extendable handle. These hardshell carrying cases offer an exterior which is molded from nearly indestructible ABS polymer. The interior consists of custom fit, high density foam to keep the

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Astronomy TECHNOLOGY TODAY

NEWPRODUCTS/INDUSTRYNEWS

IP4AP Warren Keller and Ron Brecher to Host PixInsight Workshop in Dallas, Texas Warren Keller and Ron Brecher with IP4AP are teaming up again to present a three-day PixInsight workshop in Dallas, Texas on March 22-24, 2019. The workshop will be held at Spring Creek Academy, 6000 Custer Rd., Bldg. 5, Plano, TX, 75023, USA and is limited to 30 attendees.

If you're new to image processing, PixInsight is a very powerful and much less expensive alternative to Photoshop. It is an image processing platform specialized in astrophotography, available natively for FreeBSD, Linux, Mac OS X and Windows operating systems.

PixInsight is both an image processing environment and a development framework.

It is the result of a dynamic collaboration between like-minded astrophotographers and software developers, who are constantly pushing the boundaries of astronomical image processing.

New modules are being added all the

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Astronomy TECHNOLOGY TODAY

time, eliminating the need for astro-specific, 3rd-party plugins as with Photoshop.

Because it was specifically designed for astrophotography, it has definite advantages over Photoshop and its postprocessing abilities now equal or surpass Photoshop in many areas.

PixInsight was created by Pleiades Astrophoto, a software development company based in Spain. The company works to provide cutting edge image processing and analysis tools for a broad range of technical imaging applications.

The introductory-level three-day PixInsight workshop will focus on the following objectives: • Provide a comfort level in the PixInsight working environment • Demonstrate a simple workflow to produce images from raw data • Reveal intermediate techniques for further improving images

• Build skills by processing data with individual coaching from the instructors.

While the course is aimed at those nearer the beginning of their PixInsight journey, astrophotographers of all skill levels will pick up new tips and tricks for successful deep-sky astro-image processing. Day 1 focuses on learning the user interface and processing environment and takes a simple data set through a complete processing workflow.

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Early bird registration for the workshop is $550US through January 10, 2019. Go to www.ip4ap.com for a detailed agenda, accommodation information, and to register for the workshop.

NEWPRODUCTS/INDUSTRYNEWS

CLEARLINE TECHNOLOGY CORPORATION New Boot-Up Emulator for the Meade LX200 Hand Controller

New Boot-Up Emulator for the Meade LX200 Hand Controller Clearline Technology Corporation has made available a new Boot-Up Emulator for the Meade LX200 Hand Controller.

When the LX200 Classic with version 3.xx software starts up, it expects a "handshake" with its hand controller.

Without that conversation, the telescope will not complete its start up, and thus cannot be used even by sending commands through the RS-232 port.

The new boot up emulator plugs into the keypad port in place of the hand controller and completes the start-up handshake so the telescope can respond to control through the RS-232 port. Note that this "Boot-Up" emulator has no buttons and cannot control any telescope functions by itself.

The controller provides computer control of the telescope through its RS232 port, without the Meade hand controller. It provides the ability to use all of the telescope's RS-232 command language features, with a laptop and a suitable third-party software package.

The emulator is small and stays out of the way while in place. It will blink a red LED three times after power on, when the start-up handshake has completed successfully. The controller package includes a short cable. You can also use the original handset cable.

It is available for 8", 10", and 12" LX200 "Classic" telescopes, and

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Astronomy TECHNOLOGY TODAY

LXD650/750 mounts with version 3.xx software. The cost of the emulator is $26US and is available at www.clearline-tech.com. The company ships to the US and internationally.

In addition to the emulator, Clearline provides two other useful LX200 electronic parts including a Motor Encoder Board - LX200 Classic/LXD650/LXD750 and a Calibration Tool for LX200 Motor Encoder Board.

Motor Encoder Board - LX200 Classic/LXD650/LXD750 This new-design circuit board is a replacement for the original RA and DEC motor encoders in the 8", 10", and 12" Meade LX200 "Classic" telescope. It also fits the Meade LXD650 and LXD750 telescope mounts. Each board is conservatively designed for reliability, offers ease of calibration due to potentiometer adjustment range and is fully tested prior to shipment.

Note that installation will require re-soldering connecting wires on the left-hand side of the board. The new board will also need to be calibrated by adjusting the two trim potentiometers RV1 and RV2. That adjustment should be done with an oscilloscope or DVM to verify duty-cycle of 50% on the output waveforms. There are several references on the web (included in the product documentation) that explain

how to perform the calibration procedure. For a simpler alternative, Clearline offers an Encoder Calibration Tool (more about the tool below), which is an inexpensive daughter-board that assists the duty-cycle adjustment without instruments.

The motor encoder board is priced at $28US.

Calibration Tool for LX200 Motor Encoder Board With this small board mounted between your motor encoder and its mating cable, you can adjust the output duty cycle. LEDs above the encoder's trim potentiometers indicate when the proper duty cycle has been achieved.

Benefits of the board include: Colored LEDs easily show which direction (CW or CCW) to adjust potentiometers on encoder board (Indicates "green" when outputs are at desired duty cycle [45-55%]; Takes only minutes to install, calibrate, and de-install, no special instruments required; Works on both the Motor Encoder Board LX200 Classic/LXD650/LXD750 board, and the original Meade RA and DEC boards; Can be used any time to check operation of the encoder boards; and perhaps best of all, it can help extend the life of your LX200 Classic telescope It is priced at $23US.

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NEWPRODUCTS/INDUSTRYNEWS

SOUTHERN CROSS ASTRONOMICAL SOCIETY OF MIAMI 2019 Winter Star Party

The 2019 Winter Star Party "WSP" will be held at Camp Weesumkee in 2019 from February 4 – 10. The upcoming event will feature its long-awaited return to the Florida Keys as it was displaced in 2018 due to the devastating effects of Hurricane Irma. It has taken a tremendous effort to get the venue back as remembered and the hosts assure everyone that, as always, attendees will experience great skies, interesting lectures, fine vendors, and a door prize extravaganza.

Of course, for those living in cold winter climates, the event is unique in that it occurs mid-winter during the height of the Florida Keys tourist season. The warm weather, coupled with dark skies and possibly the steadiest skies in North America, attracts attendees from all over the frozen United States, Canada, and Europe giving

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Astronomy TECHNOLOGY TODAY

the event an international flavor.

The event has been held during a new moon week each February since 1984 and now approximately 650 amateur astronomers from around the world travel to the warm subtropics of the Florida Keys. During the event attendees experience nightly observing in 360 degrees of clear steady night skies, exchange information and advice on the hobby, meet SCAS members and distinguished guest speakers, shop for astronomical equipment from the finest vendors across the globe, participate in photo contests & workshops, go sightseeing in the "Conch Republic," and record the awesome beauty sparkling in

the southern night skies.

Registration for the event is $150.

Camping is available at $85 per person.

Fees for trailers, small campers or pop ups are $50 and fees for RVs 15' and larger are $130.

More information is available at www.scas.org.

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NEWPRODUCTS/INDUSTRYNEWS

10MICRON New Line of AZ-HPS Series of Mounts 10Micron has created an entire new line of premium altazimuth mounts based on the company’s popular GMHPS line of super-accurate, absolute encoder German equatorial mounts.

The AZ-HPS series of mounts use the same absolute encoder technology as the GM-HPS mounts with instrument capacities from 55 to 330 pounds. The capability to mount single, dual, triple and quad scopes is available in the AZ2000HPS, AZ3000HPS and AZ4000HPS models.

While not suitable for long-exposure imaging without the use of a rotator, these mounts are well suited for visual astronomy, planetary and short-exposure astrophotography, supernova surveys, asteroid and comet surveys, video astronomy, satellite tracking, photometric and astrometric measurements, and other scientific uses. Their extremely precise targeting and tracking (even in an alt/az configuration) are perfect for survey work.

AZ1000 HPS The AZ1000 HPS is a versatile, light and transportable mount that offers precision absolute axis-encoders; a control box with onboard-intelligence (Linuxprocessor); V. 2 – HPS version firmware, standalone system (no PC required); professional hand control unit with graphic display and temperature control;

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Astronomy TECHNOLOGY TODAY

Losmandy 3″/Vixen GP dovetail plate; integrated WiFi; cables; counterweight bar and a strong transport carton-box with shaped foam.

SPECIFICATIONS INCLUDE: Weight: 19.5 Kg (43 lbs) Instrument payload capacity: 25 Kg (55 lbs) Counterweight shaft: 30mm diameter, stainless steel Axes: 30 mm diameter, alloy steel Bearings: Pre-loaded tapered roller bearing Worm wheels: 250 teeth, 125 mm diameter, B14 bronze Worm screw: 20mm, tempered alloy steel, grinded and lapped Transmission system: Backlash-free system with timing belt and automatic backlash recovery Motors: 2 axes servo brushless

Power supply: 24 V DC Power consumption: ~ 0,5 A while tracking ~ 3 A at maximum speed ~ 4 A peak Go-to speed: Adjustable from 2°/s to 15°/s Pointing accuracy: < 20” with internal multiple-stars software mapping Average tracking accuracy: < +/− 1" typical for 15 minutes (< 0.7" RMS) with internal multiple-stars software mapping and compensation of flexure and polar alignment errors Security stops: +/− 150° in AZ (software) +/− 155° in AZ (mechanical); +/− 95° in Alt (software) +/− 100° in Alt (mechanical) Operational temperature range (standard): - 15° C to + 35° C (+ 05° F to + 95° F) Storage temperature range: - 40° C to + 50° C (- 40° F to +122° F) Communication ports: RS–232 port; GPS port; autoguide ST-4 protocol port; Ethernet port AZ2000 The standard version allows the assembly of the optics to only one side of the mount and is supplied with a short counterweight bar. An option is available for a dual telescope configuration.

Interestingly, the AZ2000 was produced for a customer in a one-off special “Antarctica” version, which was able to

NEWPRODUCTS/INDUSTRYNEWS work at the extreme low temperature of 84°C (-119F). Special mechanical and electronic considerations were necessary in order to design and produce this peculiar mount: from the correct choice of material and sizes to the use of special and very expensive lubricants, wiring and connectors. A special housing was also designed to protect against temperature and ice crystal formation and which needed different levels of seals depending on the effective operational temperature.

10Micron can produce the AZ2000 mount for low temperature operations upon request.

The mount offers precision absolute axis-encoders; a control box with onboard-intelligence (Linux-processor); V. 2 – HPS version firmware, standalone system (no PC required); professional hand control unit with graphic display and temperature control; Losmandy 3″/Vixen GP dovetail plate; integrated WiFi; cables; counterweight bar and a strong transport carton-box with shaped foam.

SPECIFICATIONS INCLUDE: Weight: 30kg (66lbs) Instrument payload capacity: 50 kg (110 lbs) Latitude Range: 23° - 70° Azimuth Fine Adjustment Range: +/10° Counterweight Shaft: 40mm diameter, stainless steel, weight 9 lbs (4 kg) Axes: 50mm diameter, alloy steel Bearings: Pre-loaded tapered roller bearings Worm wheels: 215 teeth, 172mm diameter, B14 bronze Worms: Diameter 24mm, tempered allow steel, ground and lapped Transmission system: Backlash-free system with timing belt and automatic backlash recovery Motors: AC servo brushless Power supply: 24 VDC Power consumption: Approx. 0.7A while tracking, Approx. 3A at maximum speed, Approx. 5A peak Goto speed: Adjustable from 2°/sec. to 20°/sec.

Pointing Accuracy: < 20" with internal multi-star software mapping Average Tracking Accuracy: Approx.

1" typical for 15 minutes; Approx. 0.6" RMS with internal 25-star software mapping and compensation of flexure and polar alignment errors Safety stop: +/- 150° past meridian in RA (software); +/- 95° past meridian in RA (mechanical) Communications Ports: RS-232 port, GPS port, autoguide ST-4 protocol port, Ethernet port

AZ 3000 The new AZ3000 HPS also offers the option for option for a dual telescope configuration and can be provided as a special order for low temperature operations.

The mount offers precision absolute axis-encoders; a control box with onboard-intelligence (Linux-processor); V. 2 – HPS version firmware, standalone system (no PC required); professional hand control unit with graphic display and temperature control; Losmandy 3″/Vixen GP dovetail plate; integrated WiFi; cables; counterweight bar and a strong transport carton-box with shaped foam.

SPECIFICATIONS INCLUDE: Weight: 65 kg (143 lbs) Instrument payload capacity: 100 kg (220 lbs) Azimuth fine adjustment range (for initial orientation): +/− 10° (continued on page 26)

Astronomy TECHNOLOGY TODAY

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NEWPRODUCTS/INDUSTRYNEWS

10MICRON (continued from page 25) Counterweight shaft: 50 mm diameter, stainless steel Axes: 80/50 mm diameter, alloy steel Bearings: Pre-loaded tapered roller bearing Worm wheels: 315 teeth, 247 mm diameter, B14 bronze (AZ); 255 teeth, 192 mm diameter, B14 bronze (Dec) Worm screw: 32mm and 24mm, tempered alloy steel, grinded and lapped Transmission system: Backlash-free system with timing belt and automatic backlash recovery Motors: 2 axes servo brushless Power supply: 24 V DC Power consumption: ~ 1 A while tracking ~ 3 A at maximum speed ~ 5 A peak Go-to speed: Adjustable from 2°/s to 12°/s; Special version 48V: from 2°/sec to 20°/sec Pointing accuracy: < 20” with internal multiple-stars software mapping Average tracking accuracy: < +/− 1" typical for 15 minutes (< 0.7" RMS) with internal multiple-stars software mapping and compensation of flexure and polar alignment errors Security stops: +/− 150° in AZ (software) +/− 155° in AZ (mechanical); +/− 95° in Alt (software) +/− 100° in Alt (mechanical) Operational temperature range (standard): - 15° C to + 35° C (+ 05° F to + 95° F) Storage temperature range: - 40° C to + 50° C (- 40° F to +122° F) Special operational temperature range: Optional, for very low temperature operations Communication ports: RS–232 port; GPS port; autoguide ST-4 protocol port; Ethernet port AZ4000 The AZ4000 is capable of carrying a single instrument of up to 150kg (330lbs). The mount is available in a double telescope version which allows the use of 2 to 4 optics in a side by side

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Astronomy TECHNOLOGY TODAY

setup with a capacity of 250kg (550lbs), optimizing the load of the mount and taking advantage of the altazimuth configuration. The mount can be provided as a special order for low temperature operations.

The mount offers precision absolute axis-encoders; a control box with onboard-intelligence (Linux-processor); V. 2 – HPS version firmware, standalone system (no PC required); professional hand control unit with graphic display and temperature control; Losmandy 3″/Vixen GP dovetail plate; integrated WiFi; cables; counterweight bar and a strong transport carton-box with shaped foam.

The AZ4000 HPS Mount is available in a special 48 V version in order to reach a faster slewing speed of 12°/sec.

SPECIFICATIONS INCLUDE: Weight: 125 kg (276 lbs) Instrument payload capacity: 150 kg (330 lbs) for standard single telescope configuration; 150 + 100 kg (330 +220 lbs) for optional dual telescope configuration Azimuth fine adjustment range (for initial orientation): +/− 10° Counterweight shaft: 60 mm diameter, stainless steel, weight 13 kg – 29 lbs Axes: Azimuth: 85mm diameter; Alt 80mm diameter, alloy steel Bearings: Pre-loaded tapered roller bearing Worm wheels: Azimuth. 430 teeth, 330

mm diameter, B14 bronze; Alt. 315 teeth, 244 mm diameter, B14 bronze Worm gears: Diameter 32mm, tempered alloy steel, grinded and lapped Transmission system: Backlash-free system with timing belt and automatic backlash recovery Motors: 2 axes servo brushless Power supply: 24 V DC (48V DC as special option) Power consumption: ~ 1,5 A at sidereal speed; ~ 4 A at maximum speed; ~ 5 A peak Go-to speed: Adjustable from 2°/s to 8°/s (6°/s in R.A.); Special version 48V DC from 2°/s to 12°/s (10°/s in R.A).

Pointing accuracy: < 20” with internal multiple-stars software mapping Average tracking accuracy: < +/− 1" typical for 15 minutes (< 0.7" RMS) with internal multiple-stars software mapping and compensation of flexure and polar alignment errors Security stop: +/− 150° in AZ (software) +/− 155° in AZ (mechanical); +/− 95° in Alt (software) +/− 100° in Alt (mechanical) Operational temperature range (standard): - 15° C to + 35° C; + 05° F to + 95° F Storage temperature range: - 40° C to + 50° C; - 40° F to +122° F Special operational temperature range: Optional, for very low temperature operations (until -35°C / 31°F) An Overview of HPS Technology HPS means “High Precision and Speed.” 10Micron has provided the following overview of the HPS technology.

The AZHPS mounts feature two high-precision absolute encoders mounted directly on each axis to ensure unprecedented pointing and tracking accuracy, and high-performance servo motors and drivers for high speed pointing. (continued on page 28)

TELEPHONE 512-259-9778 WEBSITE www.scopestuff.com EMAIL Support@scopestuff.com Scopestuff is your primary source for all of the stuff you need for a great observing experience! Most orders ship the same day and prices include shipping in the USA! Our website includes hundreds of items including: CHECK OUT OUR “GEAR FINDER”!

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NEWPRODUCTS/INDUSTRYNEWS

10MICRON (continued from page 26) In the vast majority of applications, including long exposure deepsky imaging, the need for autoguiding is eliminated. The pointing accuracy allows you to be confident that, once the mount is properly setup, objects will be centered in the smallest field of view, even with a mobile setup.

Furthermore, the internal electronics allows the mount to do almost everything without the need for an external PC. The encoder system The absolute encoders provide high-accuracy, sub-arcsecond feedback to the motion of the mount. The absolute encoders render the axes “live” and free to react also to any external forces like wind and vibrations or accidental contact. This feedback is provided regardless of any zeroing or homing procedure.

This means that the electronics will always know the position of the mount. You may move the mount with the clutches unlocked and the elec-

tronics powered off, lock the clutches in any position and switch on the mount: the electronics will know where the telescope is looking. You may effectively use the mount as a Dobsonian telescope with manual pointing, retaining the full, sub- arcsecond accuracy of the encoders. This means ease of use when operating in the field, since the setup procedure is much faster.

With regard to the right ascension axis, virtually all the mechanical error from the reduction gearing is eliminated. Not only the “Periodic Error”, which comprises the periodic irregularities due to imperfection in the manufacturing and assembling of the worm, but also the non-periodic errors due to imperfections in the wormwheel, bearings, belts and so on.

With regard to the declination axis, it may seem that the encoder system is less important, since there is no sidereal tracking motion. The company points out that the declination axis is critical to sidereal tracking. If you

want to compensate for refraction, telescope and mount flexure and so on, you will have to move the declination axis at very small speeds. While the right ascension axis works always at the same speed (plus or minus small corrections), the declination axis works always at near-zero speeds, with the occasional inversion of the direction of motion. This means that mechanical backlash, belt flexure and friction forces show in the declination axis.

The company says that the system eliminates the need to find ways to minimize the effect of these forces in traditional mounts such as: having very small preload on the worm, with the risk of uncontrolled motion when the telescope is subjected to even small external forces, because of the disengaging of the worm from the wormwheel; painstakingly calibrating software backlash compensation procedures; and manually adjusting the meshing of gears or introducing forcefully small alignment errors, to force autoguide corrections always in the same direction.

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Astronomy TECHNOLOGY TODAY

NEWPRODUCTS/INDUSTRYNEWS Tracking objects and mount modelling The task of tracking astronomical objects can be decomposed into several sub-tasks including.

• Modelling the orientation of the mount with respect to Earth.

• Modelling the orientation of the telescope with respect to the mount.

• Modelling the errors of the mechanical system with respect to an “ideal” one.

• Modelling the influence of the atmosphere on the path of light rays.

• Modelling the orientation of Earth.

• Modelling the motion of astronomical objects themselves.

In order to obtain the sub-arcsecond tracking accuracy of HPS mounts, 10Micron says that all of these factors must be taken into consideration.

Modelling the orientation of the mount with respect to Earth An ideal equatorial mount has its right ascension axis pointed directly at the celestial poles. If there are errors with this, the mount will exhibit various pointing and tracking errors, in both axes, varying across the sky. So, with a typical mount that tracks objects by setting a constant velocity on its right ascension axis, it is of utmost importance to approach this ideal situation.

There are many methods for achieving this, from the universal Bigourdan method, to iterative methods exploiting the capabilities of computerized mounts, to the traditional polar scope. Many computerized mounts allow you to point to one, two or three stars, with less and less assumptions on the correctness of the initial alignment and compute the polar misalignment. This information is then used for pointing at objects.

The HPS mounts can do the same as with these methods, with the additional usage of this piece of information for correcting the tracking of objects. This means that tracking objects will always be correct, even if the mount is not aligned to the celestial pole. You may want to ensure a reasonably correct

alignment to avoiding field rotation on long sequences of imaging. Various functions are provided by the 10micron firmware: even the number of turns you must apply to the adjustment handles for the azimuth and altitude is given.

So the HPS technology eliminates the polar scope to the advantage of mechanical stiffness of the mount, since the initial alignment can be done with the mount misaligned even by many degrees from the pole, and approximately centering two bright stars in the eyepiece (using even manual movements, like in a Dobsonian), then centering a third star with the adjustment handles.

All of this requires a reasonably accurate knowledge of time and your location on Earth. If you plan to reuse the alignment later (for example if you are in an observatory), you will have to keep the mount’s clock accurately synchronized and use very precise coordinates for your site. For this reason, beyond the usual data entries from the keypad or with an external PC, 10Micron mounts support reading all these data from an optional GPS module.

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Modelling the orientation of the telescope with respect to the mount Your telescope’s optical axis will not be perfectly perpendicular to the declination axis, and it will not be perfectly aligned with the zero angle of the absolute encoder. When you add the third star to the alignment procedure, these errors are automatically computed and corrected in the future.

Modelling the errors of the mechanical system with respect to an “ideal” one Even with high-accuracy encoders mounted directly on the axes, there is still the issue of mechanical flexure. In a number of mounts the mechanical errors are not dealt with at a software level.

While mechanical errors can minimized through careful designing and manufac(continued on page 30)

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NEWPRODUCTS/INDUSTRYNEWS

10MICRON (continued from page 29) turing, as the company points out, if you allow for an error of one arcsecond during the exposure of an image, a little calculation will show that this error can be introduced by a deformation of a leg of the typical tripod of just 5 thousandths of a millimeter. A deformation like this can be easily caused just by moving around the barycenter of a non-perfectly balanced telescope.

The HPS system accounts for the mechanical flexure of the mount and telescope. It does so by pointing to various locations in the sky, and comparing them against the encoder readout (i.e., the absolute angle set on the mount’s axes). With enough points, flexure can be modeled well enough to allow for high-precision pointing.

With 10micron mounts, the procedure can be as simple as adding stars to the ones you already used for the initial

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Astronomy TECHNOLOGY TODAY

alignment. This can be automated in a very efficient way by using external tools that point to a predefined set of locations in the sky, take a picture, measure the exact coordinates by a process called “plate solving” and feed the coordinates back to the mount. You can use up to 100 alignment stars/points for this task, and everything can be done in a surprisingly little amount of time, thanks to the high pointing speed.

All of this works if mechanical errors are repeatable. This means that, while mechanical flexure can be usually modeled with excellent accuracy, this doesn’t apply to mechanical play or backlash.

The on-axis encoders ensure that no backlash in the mount will get in your way while creating a pointing model, tracking or pointing objects, while you have the task of eliminating flopping mirrors, loose focuser tubes and so on.

Modelling the influence of the atmosphere on the path of light rays Atmospheric refraction is the result of the earth’s atmosphere bending the rays of light from astronomical objects, depending on air density. With traditional mounts, often it is advised to point the right ascension axis to the refracted celestial pole, and set a special tracking speed that compensates for the apparent speed difference due to refraction (in right ascension only).

10micron mounts allow for setting of the barometric pressure and atmospheric temperature, and offer the ability to incorporate changes in these during an observation session, in order to continuously correct their pointing and tracking to account for atmospheric changes. This can be done manually, with the keypad, or from an external PC.

NEWPRODUCTS/INDUSTRYNEWS Modelling the orientation of Earth The earth rotates with respect to astronomical objects.

By far, its main motion is the daily rotation. So, for being called an “equatorial mount”, often it is enough to provide a constant-rate rotation around the right ascension axis. This rate usually is given by a quartz clock, and so it should be reasonably accurate. However typical quartz oscillators used in electronics (and also in a typical PC) are not temperature compensated. At a fairly typical temperature of -5°C (23°F), which is not rare for astronomical observation, a typical quartz can have an error of tens of parts per million (ppm).

Errors of 20 or 30 ppm are commonly observed, which would cause errors in right ascension accumulating at about 2.5 seconds per day, which means more than one arcsecond per hour. The loss of pointing precision in a 12-hour winter night would be of about 20 arcseconds, and much more if the mount is shut down and powered on days later.

This can be corrected by keeping the mount always synchronized to an external time source, like a standard PC with its clock synchronized to the NIST time servers, or with the optional GPS module. All 10Micron motor drivers feature a battery-backed clock with temperature compensation, which is able to keep time with an accuracy of 3.5 ppm from –40°C to +40°C (–40°F to +104°F).

A much slower, but nevertheless fundamental, movement is the precession of equinoxes. If you don’t model the precession, you are forced to use standard coordinates (for example, when doing alignment).

Precession changes the direction of the Earth’s rotation axis, i.e. the celestial pole, and some systems do not account for precession in their databases. By default, 10Micron mounts work in JNOW when communicating with the outside, i.e. the coordinates you read and set in the keypad are referred to the true equinox of the date of observation.

Everything is accounted for in the firmware, even nutation and light aberration.

Another factor which can limit the accuracy of the mount over long periods is the change in Earth’s rotation rate. What we call the “UTC time” is only an approximation to the angle of rotation of Earth. The angle of rotation of Earth is measured by UT1, if we neglect the pole wandering and seasonal variations, (that amount to less than one arcsecond). UTC is based on atomic clocks, and sometimes a socalled “leap second” is inserted into it to maintain it within 0.9 seconds of UT1.

So, when you approximate UT1 with UTC, you may introduce a difference of up to 14 arcseconds into your pointing accuracy. This difference changes very slowly, so that the degradation of pointing models (simply due to terrain creeping and other “very slow” things) is always faster than this change, and you will not notice any problem in (continued on page 32) Astronomy TECHNOLOGY TODAY

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10MICRON (continued from page 31) practice. But when the leap second is inserted, you have a sudden jump in coordinates. 10Micron has implemented a full accounting of UTC, UT1 and leap seconds since firmware revision 2.13.1.

Modelling the motion of astronomical objects themselves Quite a number of astronomical objects exhibit a visible movement including planets, asteroids, comets, and artificial satellites of the Earth. The firmware of 10micron mounts can compute the motion of all these objects directly from their orbital parameters (except for planets, you will have to upload orbital parameters into the mount).

Why not autoguiding? It seems simpler…

For the user, autoguiding means additional work. When using an external guider scope, you can’t compensate all flexures between the two instruments, and you have additional, heavy equipment. When using a dedicated guider camera, it means additional cabling, software installation, setup and searching for suitable guide stars, looking for customized guiding software parameters, and calibration. HPS mounts can be aligned to bright stars during twilight, then every second of darkness can be used for imaging. For those who prefer autoguiding capabilities, mounts provide a standard ST4 port, as well as all the usual settings and controls by remote software.

Pointing objects HPS mounts feature a very rich database of objects, including the classical Messier and NGC/IC catalogues, as well as many catalogues of stars, including variables and doubles, and of deepsky objects. Also, a catalogue of moon

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Astronomy TECHNOLOGY TODAY

features is available and useful thanks to the high pointing accuracy.

The high speed of the mount is necessary, beyond speeding up the alignment procedures, for fast satellites catching (especially after a meridian crossing). Furthermore, it helps to reduce loss of time in research applications, increasing the amount of data that can be obtained in the often short observing nights.

Instrument setup The HPS mounts feature a variety of accessories for mounting various instruments. Even multiple instruments can be mounted on a single mount, in order to have the right imaging equipment always ready. Since the pointing and tracking model depends on the specific instrument (the flexure is different), the mount allows for different models, one for each instrument, that can be saved in the internal memory and reloaded when required.

Another useful feature, especially for heavier mounts, is the electronic balance function. With this function you may measure the unbalancing of the instrumentation and adjust accordingly. The high speed is very useful also in quickly accomplishing up this procedure.

Remote operation and connectivity The HPS mounts offer a number of connecting options. While you may choose the traditional RS-232 connection to control the electronics from an external PC, you may prefer to dedicate it to directly controlling a computerized dome. The firmware will provide all the relevant computations, even for mounts that are mounted off-center and instruments mounted with offset.

The GPS port doubles as an additional RS-232 port, if you don’t use the GPS. The recommended way of

connecting the mount to your PC is using the LAN connection, via TCP/IP, or the Wireless connection. The mount can connect to an existing WLAN, or it can be used as a hotspot to which your PC, tablet or smartphone can connect.

The LAN connection offer superior high-voltage tolerance with respect to the typical RS-232 connection; this is even better with the WLAN which is wireless.

In case of remote observatories, which are subject to lightning, this may make the difference between healthy electronics and a fried ones!

The mount supports up to ten simultaneous TCP/IP connections, so you can use different software and different devices at the same time. 10micron provides an ASCOM driver for Windows, but if you want to implement your own control system, they provide the command set that can be used both on the RS-232, LAN and WLAN connections. The command set is largely LX200 compatible and also includes many more functions and operating modes. In remote operation, there is the additional security provided by the absolute encoders - in no case you will lose your alignment, even in case of slipping clutches.

The HPS mounts are able to operate up to 30° beyond the meridian, in both directions (this means with the counterweight bar up and the telescope down).

This allows at least an arc of 60° for tracking every object, corresponding to at least four hours of tracking for objects crossing the meridian (provided that the object doesn’t set or encounter another limit). This amount is configurable from 0° to 30° to obtain the maximum flexibility. The mount will warn you when it is reaching tracking limits and when at the limit, tracking will stop. You will have to point the object again to force a meridian flip.

NEWPRODUCTS/INDUSTRYNEWS

Astronomy TECHNOLOGY TODAY

37

NEWPRODUCTS/INDUSTRYNEWS

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Astronomy TECHNOLOGY TODAY

tracker and spaceflight simulator.

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EXPLORE SCIENTIFIC 68° AND 82° EYEPIECES

Image 1 - Explore Scientific 68° 16mm (left) and 82° 14mm (right) eyepieces. Each come with top and bottom dust caps in a foam-padded Explore Scientific box.

In a recent Astronomy Technology Today article (ATT, volume 12, issue 3), Gary Parkerson provided his insight on the new Explore Scientific 68° and 82° eyepieces. In this article, I will provide a different prospective on why I like these great eyepieces!

When I first bought my first telescope in the 1970, there were many types of eyepieces to choose. The designs had names like Ramsden, Erfle, Huygen, Kellner, König and Orthoscopic, to name a few. Each had pros and cons. Eye relief, exit pupils, and field of view

WHY I LIKE THESE GREAT EYEPIECES!

By Dr. James Dire

(FOV) were much smaller than today’s offerings. I still have my favorite 18mm Orthoscopic and a few Ramsdens. The Orthoscopic is great for viewing planets and Ramsdens are still the safest (for the eyepiece) design to use for solar projection.

In the 1980s, Plössl eyepieces started showing up everywhere and became very popular. Plössl provided a then large 50° or more apparent FOV. With high quality glass and lens coatings, Plössls provide high-contrast, symmetric views. They still are made and sold today.

I predominantly used Plössl eyepieces in the 1980s and 1990s. Then I discovered Tele Vue Nagler eyepieces. I felt Naglers were the best eyepieces made. Many longer focal length Naglers came with 2-inch barrels. They all have great eye relief, large exit pupils and an 82° FOV. The quality is superb. I owned 31mm, 26mm, 22mm, 20mm, 12mm, 5mm and 4.8mm models.

More recently, I tested some Tele Vue Ethos eyepieces along with my Naglers. The 100° FOV is quite impressive, almost too much to take in. The FOV is so large I have to pan my eyeball around to see everything the eyepieces capture.

Astronomy TECHNOLOGY TODAY

39

EXPLORE SCIENTIFIC 68° AND 82° EYEPIECES

Image 2 – This view shows the wide diameter lenses comprising both eyepieces.

Image 3 – This view shows the size of the Explore Scientific 68° 16mm and 82° 14mm eyepieces compared to two brands of 15mm Plössls, a Tele Vue 9mm Nagler and a Tele Vue 13mm Ethos eyepieces.

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Astronomy TECHNOLOGY TODAY

I eventually traded in my 12mm Nagler for a 13mm Ethos to use with my 14-inch f/6 Dobsonian telescope. My 12mm yielded 178x with this telescope. Even with the eyepiece’s 82° FOV, objects did not stay in the eyepiece very long before I needed to nudge the telescope. With the 13mm Ethos, the magnification is slightly lower (164x). Aided by the 100° FOV, objects are in the eyepiece much longer without moving the telescope.

Today I predominantly use three Tele Vue eyepieces: the 2-inch 26mm Nagler, the 2inch 13mm Ethos and the 1.25-inch 5mm Nagler.

My Nagler and Ethos eyepiece are superb, and I feel are the best I have ever used.

However, I have had two challenges with them. First, several of my telescopes do not have enough back focus range for the longer focal length (12mm and longer) eyepieces to focus. Therefore, I have to use a focuser extended. Second, the 2-inch eyepieces are heavy. They are so heavy that I cannot use them with my 70mm apo (see ATT, volume 11, issue 2) on my iOptron Cube Pro (see ATT, volume 10, issue 6) mount. They are also heavy with my 190mm Mak-Newt (see ATT, volume 11, issue 6), since I use rotating tube rings with that telescope. The weight of the eyepieces causes too much rotational torque on the tube.

Thus, I began a search for some high quality 1.25-inch eyepieces to augment my arsenal of 2-inch eyepieces. I did a lot of research and decided to try out Explore Scientific 68° and 82° eyepieces.

Image 1 shows the two eyepieces I purchased. On the left is the 14mm 82° eyepiece and on the right is the 16mm 68° eyepiece.

Each came in the typical foam-padded Explore Scientific box with the decorative starchart covers. They also came with top and bottoms dust caps.

To achieve the wide FOV, eliminate chromatic aberration, and provide sharp flat fields, these eyepieces use 6-7 elements of dense crown, light crown, dense flint, and lanthanum optical glasses. The eyepieces are waterproof and sealed with inert argon gas between the elements. The argon purges any moisture that might condense on the lenses

EXPLORE SCIENTIFIC 68° AND 82° EYEPIECES during cold weather use.

The eyepieces are ruggedly manufactured with high quality materials. Each are serrated for ease of gripping either barehanded or with winter gloves. The eyepieces come with rollup rubber eye guards that can be removed and easily replaced if they become worn.

The 16mm 68° eyepiece is 62mm tall, 43mm wide and weighs 158g (5.5 oz.). The eye relief is around 12mm with a field stop diameter of 18mm. Although the focal length is smaller, the 14mm 82° eyepiece is the larger of the two. It is 83mm tall, 48mm wide and weighs 256g (9.0 oz.). It has 15.6mm of eye relief and a field stop diameter of 18.9mm. In a 1000mm focal length telescope, the 14mm provide 71.4x magnification, while the 16mm provides 62.5x. Image 2 shows the top of the eyepieces with the generous diameter of the glass.

Image 3 shows the two eyepieces standing next to several other eyepieces for comparison. Bracketing the Explore Scientific eyepieces are two Plössl eyepieces with similar focal lengths. One is a Tele Vue Plössl, while the other is a generic Plössl. In addition, the photo shows a 9mm (borrowed) Tele Vue Nagler and a 13mm Tele Vue Ethos eyepieces.

While the Explore Scientific eyepieces are notable beefier than the two Plössls, the Nagler and Ethos eyepieces dwarf them.

The true field of view of an eyepiece is calculated by dividing the apparent field of view, in this case 68° or 82°, by the effective magnification. It ends up both Explore Scientific eyepieces provide the same true FOV. The true FOV for 1000mm focal length telescope is 1.1° (82 ÷ 71.4 or 68 ÷ 62.5). So I expected to see the same view when interchanging them in the focuser, with the exception of the field being more spread out in the 82° eyepiece. And that’s exactly what I saw.

I tested each eyepiece in a 132mm f/7 apochromatic refractor and in a 190mm f/5.3 Maksutov-Newtonian reflector. Not only did I compare the eyepieces to each other, but I also compared them with a 13mm Tele Vue Ethos eyepiece, a 9mm Tele Vue Nagler eyepiece and a 15mm Tele Vue Plössl eyepiece (Image 3). The former and the latter of those Astronomy TECHNOLOGY TODAY

41

EXPLORE SCIENTIFIC 68° AND 82° EYEPIECES

Image 4 – The authors complete set of 1.25-inch barrel Explore Scientific eyepieces and the 2-inch barrel Tele Vue Nagler eyepiece.

Image 5 – The 24mm Explore Scientific eyepiece and the 26mm Nagler eyepiece.

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Astronomy TECHNOLOGY TODAY

three provided comparable magnification, while the 9mm resulted in a noticeable higher power, Both Explore Scientific eyepieces provide sharp, high contrast views with pinpoint stars throughout the FOV. The same was true with the 9mm Nagler and the 13mm Ethos. The views through all four were superior to the 15mm Plössl, where the stars were not as sharp near the edges.

Both the 68° and 82° Explore Scientific eyepieces performed splendidly. The choice of whether to use the 68° and 82° Explore Scientific eyepieces boils down to two factors.

One is FOV. I prefer the wider FOV of the 82° eyepiece over the 68° eyepiece. The other factor is cost. The 82° cost more than the 68° eyepieces. Buyers must weigh those two factors before purchasing.

After testing the two 68° and 82° Explore Scientific eyepieces, I decided to stick with the 82° eyepieces and bought two additional ones. My set now consists of the 6.7mm, the 8.8mm, and the 14mm. I also wanted one around 24mm to use in lieu of my similar focal length, but much heavier 26mm Nagler.

The Explore Scientific 24mm 82° did not come in a 1.25-inch barrel option, so I went with the 68° 24mm eyepiece. My complete set of Explore Scientific eyepieces is shown in Image 4.

Image 5 shows the 24mm Explore Scientific and the Tele Vue 26mm Nagler. They perform equally well in my telescopes, although the 24mm has a smaller apparent field of view.

My Tele Vue eyepieces will still be my workhorse oculars when using my 14-inch Dob; my 132mm apo; and with my 70mm apo, when I have it mounted piggyback on a larger instrument or by itself on either my Celestron CGEM II or AVX mounts.

However, my new set of 82° Explore Scientific 1.25-inch eyepieces will be my primary eyepieces when using my 190mm Mak-Newt, or when I am travelling light with my 70mm apo with either my iOptron Cube Pro mount or my Explore Scientific Twilight II mount. I think I am finally set for life with high quality telescope eyepieces!

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COMET 21P/ GIACOBINI-ZINNER IMAGING A VISIT FROM AFAR

By Matt Harmston

Though comet 21P/Giacobini-Zinner (21P) last trekked through the inner solar system a mere 6.6 years ago, this summer marked the first time I had heard the name. There I was, wondering when I’d get to image a comet, when I heard the news: 21P would pass in front of Messier 35 in the wee hours of Saturday, September 15, 2018.

Some 20 years ago, M35 was the first open cluster toward which I trained my first telescope. Could I be so lucky as to include an old friend like M35 in my first cometary image? Dad always said, “luck is what happens when preparation meets opportunity.” Hmm… luck might come my way.

Saturday morning’s 0200 alarm clamored with painful intensity, yet the subsequent brain fog was unable to stifle my trepidation as I peeked out the window: Would a “mostly clear” forecast at bedtime result in haze, smoke, or the occasional cloud? Would the forecast simply be wrong? To my coffee-deprived delight, the skies were a little hazy but not bad at all. I was going to image my first comet!

Let’s Meet 21P/ Giacobini-Zinner Comet 21P wasn’t a showstopper, as it did not even reach naked-eye brightness under my semi-dark skies. However, it was well within reach of my small scope and camera setup. This

Image 1

comet isn’t particularly large, having a nucleus (i.e., the dirty snowball at the coma’s core) roughly 2km in diameter.

It’s coma (that is, the “head” that we see) consists of gas and dust presently spanning over 250,000 km (nearly twice the size of Jupiter).

At only 59 million km from Earth (just over a third of the Earth/sun dis-

tance), 21P was relatively close when I was imaging. Given its speed of roughly 39 km/s, I was quite ok with the comet keeping some distance between us.

Like most comets when they approach the Sun, 21P was sporting a tail of gas and dust streaming from the nucleus due to solar radiation pressure and Astronomy TECHNOLOGY TODAY

45

COMET 21P/GIACOBINI-ZINNER wind. Comets often have an ion tail and a gas/dust tail that may not point in exactly the same direction depending on where the comet is found in its orbit.

The description of why is beyond the scope of this article, but for 21P, the most recent information I could find suggested that the tails overlapped at the time of my imaging.

Comet Tails Point Away from the Sun Because comet tails are created when the sunâ&#x20AC;&#x2122;s radiation and solar wind erode the nucleus, they stream away from the comet in the direction opposite the sun. As a result, you might see tails being led by the coma through space, point in the direction of travel, or somewhere in between. Similarly, gas/dust tails might eventually curve as the comet traverses its orbit, as exhibited by the sweeping fan of C/2006 P1 (McNaught) in early 2007. Our comet, Image 2

46

Astronomy TECHNOLOGY TODAY

COMET 21P/GIACOBINI-ZINNER 21P, isn’t nearly that spectacular, but its tail is unmistakable.

A Chance Conjunction: Back to the Alarm clock Comet 21P passed between Earth and open cluster Messier 35 (found some 2,772 light years away, shining at magnitude 5.3) on the morning of September 15th under clear Riverside skies.

After-effects of my alarm clock’s sensory assault evaporated as I noted how readily detectable the comet’s motion was…even in just ½ hour. Even more, the images also revealed that the tail’s orientation wasn’t consistent with its direction of motion.

Though I had to battle low-altitude seeing effects and the light dome of a large local establishment, I was able to capture three stacks of images with my Mallincam DS10c and 100mm ED refractor, each using 2x2 binning. I processed the final images such that Image 3

Astronomy TECHNOLOGY TODAY

47

COMET 21P/GIACOBINI-ZINNER green light and gamma were enhanced, thereby making the tail stand out.

Image 1, completed at 0238CDT, used only a 10 second exposure to avoid artifacts due to low altitude and skyglow. M35 is centered in this image, with NGC 2158 (over 6,000 light years beyond M35) at the lower left. As you can see, the comet’s coma (or, head) is just above and left of the brightest star in M35. The tail is faint, but unmistakably extends to the left in the image.

Image 2 was completed at 0305CDT, and I was able to bump the exposure time up to 25 seconds without introducing image artifacts. Here, the

tail appears to extend further because this exposure allowed for more light to be captured. Something that I found particularly exciting (maybe I need to get out more?) was that even in this short time span, the coma had slid noticeably down since the previous image was taken, getting ever closer to M35’s brightest star.

Image 3 was completed at 0449CDT with a 35 second exposure.

As can be seen, the coma slid much further across the face of M35. Similarly, the visible tail extends nearly to the edge of the image. It is quite obvious that the tail was not simply following

the coma through space…it had it’s own direction.

Serendipity: First in a First This article’s illustration of cometary motion and tail orientation will come as no surprise to many readers …after all, I was looking for motion and tail direction myself. But, the imaging run highlights a broader, wonderful truth: The night sky is both beautiful and dynamic, something just waiting to be experienced.

Silent, subtle, yet full of wonder and awe, a tapestry of marvel and miracle reveals itself each evening. And for that, I am grateful.

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ADVENTURES IN ASTROPHOTOGRAPHY WITH SKYTOOLS 4 IMAGING

By Greg Crinklaw

In the previous issue of ATT, I described how the imaging model was developed and tested for SkyTools 4 Imaging. In this installment I am going to describe how I have put my software to use for my own imaging projects.

The ability to predict the signal for any object means that we can determine which objects are most suitable for observation. I have access to a wonderful imaging system located in the foothills of Californiaâ&#x20AC;&#x2122;s Sierra Nevada. It is a Planewave 24-inch f/6.5, equipped with an FLI PL0900 CCD camera. This is one of the many telescopes available to subscribers on iTelescope.net.

I wanted to image a distant minor planet in the outer solar system. To do this, I needed to know how faint I could image and still detect the object in a reasonable exposure time, and which minor planets would be well suited for observation that night.

Using SkyTools 4 Imaging, I searched all known minor planets, listing only those that are distant, such as Scattered Disc Objects and Cubewanos.

Figure 1 - The distant dwarf planet Orcus.

I put that list into the Target Selection Tool and told it that I was only interested in objects that could be detected in ten minutes of total exposure time, and that were well placed for observation that night. By detected, I mean that I could achieve a Signal to Noise Ratio (SNR) of 7 in ten minutes or less.

Of the objects that remained, I

picked the little-known dwarf planet Orcus. SkyTools generated an ACP plan for Orcus, selecting 2x300 second exposures in order to maximize the SNR. At the time Orcus was magnitude 19.1 and 48 AU away. Orcus, which was discovered by Mike Brown in 2004, is just under 600 miles in diameter and has a faint moon called Vanth (too close to

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ADVENTURES IN ASTROPHOTOGRAPHY WITH SKYTOOLS 4 IMAGING

Figure 2 - The dwarf planet Orcus image cropped.

Orcus for me to image).

For my next project, it seemed to me that this telescope would excel at imaging a globular cluster, so I used the

Target Selection tool to find a cluster that had a good image scale and that was well-placed at the time. SkyTools recommended M15 as my best choice.

What I had in mind was to do this image on a budget. Rather than using the full LRGB, or even RGB filters, I would only use the R and B. After all, there are no green stars. The idea was to generate a pseudo-green channel by substituting the average of the Red and Blue filters. I have had success with this in the past creating color images from the Red and Blue Digital Sky Survey images.

As I mentioned in my previous article, how much light is detected in a given filter is a complex combination of the light source, transmission of the filter, telescope optics, and spectral response of the detector. So it is difficult to know without a lot of experimenting what exposure times should be used in order to balance the Red and Blue filters.

But of course, this is exactly what SkyTools Imaging excels at. I considered the range in color of the stars in the color-magnitude diagram (Figure 2), as

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ADVENTURES IN ASTROPHOTOGRAPHY WITH SKYTOOLS 4 IMAGING told by the (B-V) color index. The brighter stars (top of diagram) are mostly on the red end, with (B-V) > 0.8 or so. There is also a group of blue stars (on the left) at around 16th magnitude.

These stars lie on what is called the horizontal branch.

I estimated that right down the middle was at (B-V) of about 0.7, so I decided that I wanted to expose for stars that are 18th magnitude with a (B-V) color of 0.7. The idea was that I would choose exposure times that would balance the Red and Blue filters, such that these stars would be about the same.

I could have chosen other criteria.

For instance, a popular approach is to expose for stars of similar color to the sun so that they will appear white or gray in the final image, better approximating the natural colors. As it turns

Figure 3 - The color-magnitude diagram for M15. Stars to the left are blue; those on the right are red.

Astronomy TECHNOLOGY TODAY

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ADVENTURES IN ASTROPHOTOGRAPHY WITH SKYTOOLS 4 IMAGING

Figure 4 - M15 as a combination of Red and Blue images. Note the smattering of fainter blue stars.

out, this is also near (B-V) of 0.7.

With my goals in mind, I set up a SkyTools Imaging project for M15 to obtain an SNR of 20 in the Red and

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Astronomy TECHNOLOGY TODAY

Blue filters for 18th magnitude stars with a (B-V) of 0.7. An SNR of 20 should produce an image of acceptable quality at 18th magnitude.

It told me that for this telescope and camera, to achieve these goals, I would need a total of five minutes in the Red filter and nine minutes in the Blue.

When it created an ACP plan for that night, it chose 3x180 second exposures in the Blue followed by 1x300 second exposure in the Red. I uploaded the plan to the telescope and waited.

As luck would have it, clouds came in and the dome was closed during the Red exposure. So I logged the Blue exposures and waited for another night.

This time SkyTools created an ACP plan for one 300 second exposure in the Red in order to complete my project. If I had it to do over again, I would have selected sub exposure times that would result in the same signal in each filter, but I think the final image came out pretty well anyhow.

My next project with this telescope was to image a planetary nebula in nar-

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ADVENTURES IN ASTROPHOTOGRAPHY WITH SKYTOOLS 4 IMAGING

Figure 5 - The Fetus Nebula (NGC 7008) in H-alpha (red channel) and OIII (blue channel).

row band filters. I didn’t want something small or faint, but at the same time I didn’t want to image something common either, like M57. I put a list of planetary nebulae into the Target Selection tool and it ultimately recommended NGC 7008, the Fetus Nebula.

Perfect!

The best configuration to use for an

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extended object is an interesting problem. There is a tradeoff to be made between image scale and exposure time. If you have the option of a focal extender or reducer, you can control the image scale, and even if you don’t, most cameras allow binning (which also alters the image scale). For example, at binx2, NGC 7008 will cover half as many pix-

els, which will reduce the amount of detail that can be recorded. But this will also cut down the exposure time needed to reach the desired SNR. Taking these things into consideration for me, SkyTools recommended binx1. I had a look at the size of the nebula at both binnings and how much longer it would take to reach the same SNR at binx1 as binx2, and came to the same conclusion. Given the relative emission line strengths of the H-alpha and OIII lines, and the properties of the optical system and camera, a total exposure time of 80 minutes was recommended in the OIII filter, and 30 minutes in the H-alpha. This is to reach my SNR goal of 25 in each filter.

Unfortunately, I was not able to reach these goals this season, and plan to take it up again next year. The accompanying image is based on what I have so far, with H-alpha in the red channel and OIII in the blue. Eventually I also intend to get RGB images of the star field in order to combine nicer-looking stars with the nebula.

For my next project, I am planning to take advantage of one of iTelescope’s new one-shot color imaging systems, located at Bathurst Observatory in Australia. I want to make a big mosaic of the Large Magellanic Cloud.

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Figure 1 - The distant dwarf planet Orcus.

ADVENTURES IN ASTROPHOTOGRAPHY WITH SKYTOOLS 4 IMAGING

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Figure 2 - The dwarf planet Orcus image cropped.

ADVENTURES IN ASTROPHOTOGRAPHY WITH SKYTOOLS 4 IMAGING

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Figure 4 - M15 as a combination of Red and Blue images. Note the smattering of fainter blue stars.

ADVENTURES IN ASTROPHOTOGRAPHY WITH SKYTOOLS 4 IMAGING

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Figure 5 - The Fetus Nebula (NGC 7008) in H-alpha (red channel) and OIII (blue channel).

ADVENTURES IN ASTROPHOTOGRAPHY WITH SKYTOOLS 4 IMAGING

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ASTRONOMY

TECHNOLOGY TODAY Your Complete Guide to Astronomical Equipment

LOOKING BACK SERIES - Vol. 7 -

2013 Issue 3

THE 16-INCH F/4.5 COLLAPSIBLE-TRUSS DOBSONIAN FROM NEW MOON TELESCOPES New Design Approaches and Old-Fashioned Craftsmanship In our Looking Back series we feature two articles about niche companies that produce hi-end, custom, and portable truss Dobs. In this article Damian Allis reviews his prized New Moon Telescopes (NMT) built by NMT owner Ryan Goodson. The line of scopes originally reviewed have now evolved into NMT’s “Hybrid” series, which you can read more about at www. http://newmoontelescopes.com.

66 Astronomy TECHNOLOGY TODAY

The 16-inch f/4.5 Collapsible-Truss Dobsonian From New Moon Telescopes

New Design Approaches and Old-Fashioned Craftsmanship

By Damian G. Allis, Ph.D.

New Moon Telescopes (NMT, newmoontelescopes.com) is a very recent addition to the list of manufacturers of custom Dobsonians, having made their first company appearance at the Kopernik Winter Star Party (kopernik.org) in January 2013 and their commercial appearance at NEAF 2013.

While NMT is now making itself

known to the larger amateur astronomy community, NMT is no secret to Central New York observers. Amateur astronomers in several CNY astronomy clubs have seen the expert woodworking skills and design choices of NMT’s owner and sole craftsman, Ryan Goodson, first-hand, giving CNY observers and their always unpredictable weather conditions the honor of

being NMT’s original customer base both in rebuilds and new Dobsonians.

My own experience with NMT goes back to the company’s beginning, as I am the proud owner of NMT #1, a “lefty” 12.5-inch Dob equipped with NMT’s current choices for premium optics and hardware. The rapid progress in NMT’s design work and prototyping can be seen in the

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THE 16-INCH F/4.5 COLLAPSIBLE-TRUSS DOBSONIAN FROM NEW MOON TELESCOPES

Image 1 - The rocker box and mirror box – pinned box joints and finish.

speed at which the original split-block design (used in NMT #1) was shelved over the course of several months in favor of a new collapsible-truss design (used in #8) that is replete with benefits over any other truss designs I’ve used or seen.

In seeing both Ryan’s early design ideas and his first NMT prototypes, I was sure my specific needs would be easy for him to meet: I wanted a scope I would have to buy

only once (that is, the last 12.5-inch scope I would ever feel need to purchase) that would survive constant traveling and group use at public viewing sessions with the Syracuse Astronomical Society and, currently, at lecturing and sidewalk astronomy outreach sessions with CNY Observers & Observing (cnyo.org).

Admittedly, I am not a “building” amateur astronomer and definitely do not

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foresee myself making the pilgrimage to Stellafane to learn how to grind a first mirror. My experiences with NMT scopes are as an avid observer who wanted portability and the perfect view in a scope that combined custom-build craftsmanship with out-of-the box assembly ease.

Ryan, who had already done the bookwork on a primary mirror, secondary mirror, focuser, and other hardware options, made my component selections for NMT #1 easy. Ryan’s recommendations were the current NMT options for fellow only-once purchasers – MoonLite Focusers, AstroSystems Spiders, Antares Optics secondary mirrors, and primary mirrors from Lightholder Optics.

Ryan’s design choices have evolved over the past few years to improve the functionality of NMT scopes, but the craftsmanship and attention to detail remain the same – NMT #1 is in as good a condition today as it was at purchase – quality components and rock-solid construction produce a scope that, in my case, remains flawless in its finish and has had zero problems of any kind going into its third year of lectures and star parties.

First Impressions I suspect that the real merit tests of appearance and, in the case of NMT’s collapsible truss, a novel contribution to

THE 16-INCH F/4.5 COLLAPSIBLE-TRUSS DOBSONIAN FROM NEW MOON TELESCOPES

Image 2 - The top of the mirror box, showing the truss locking screws, Image 3 - A side view of the crescent bearings and matte-black intemirror cover, and truss placement positions. rior of the rocker box.

Image 4 - The mirror cell and finger screws.

Dobsonian design, is the vendor floor at NEAF 2013. The NMT booth featured a customer’s 18-inch f/5, the 16-inch f/4.5, and a custom build for a new owner’s own 8-inch mirror. Comments at the booth and in subsequent online forum discussions make constant reference to the beautiful finishes and liquid-smooth motion.

The fully assembled 16-inch scope weighs under 100 pounds, is easily maneuvered by one person with its removable wheelbarrow handles, and packs up for transport in a compact car. One does not usually use “portable” to describe a 16-inch Dobsonian, but NMT has done its best to

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Image 5 - The 18-contact floating mirror cell in isolation.

balance weight and strength into a single scope. Portability is instead engineered into the design both by the reduced weight of the separate components and by the ease of assembly of the novel collapsible-truss design (in this case, “portability” also refers to the reduced hassle of getting your scope out and set up in the first place).

Zooming In After taking in the size of the scope itself, the first thing that draws the eye is the woodwork of the mirror and rocker boxes.

The craftsmanship and finish are as near perfect as one would hope to find. This vi-

sual appeal goes back to the NMT building process – one person is singularly responsible for the selection of wood, the cutting, the assembly, and the finish.

Unlike a larger manufacturing output where slight offsets in seams, tightness or looseness in mass-produced components, or slight differences in finish due to variations in the tones of the individual wood might occur, the NMT mirror box, rocker box, and secondary cage are worked jointly with the final product in mind. The pinned box (or finger) joints that define the look of the NMT mirror and rocker boxes are both visually attractive and finger-touch

THE 16-INCH F/4.5 COLLAPSIBLE-TRUSS DOBSONIAN FROM NEW MOON TELESCOPES smooth (Image 1). The result of using the pinned box joint approach is a mechanically stronger mirror box as well, an important benefit of NMT’s other selections in the 18- to 24-inch range. In the 16-inch and smaller scopes, this assembly method guarantees a rock-solid base as good at protecting the mirror as it is assuring smooth and stable scope motions.

Grade B/BB Baltic Birch Plywood is used for the construction of the rocker box (3/4-inch), mirror box (1/2-inch), and secondary cage (1/2-inch), a wood known for its strength and wear resistance. The handrubbed finishing process involves multiple single-coat and sanding steps, followed by a final hand-brushed outdoor varnish coat to produce both great wear resistance and fine grain detail on inspection.

The result is a scope that is everywhere smooth to the touch and visually attractive.

NMT offers a selection of colors, but my personal preference is the natural Baltic Birch finish, followed closely by the Colonial Maple (both of which make the box joints and darker components stand out more).

Image 6 - The three boundary layer fans and counterweight holders; placement of the potentiometer and on/off switch.

26-inch outer diameter crescent bearings (“waxing” when the scope is horizontal, “waning” when it’s vertical, Image 3). The crescent design and placement have the advantage of moving the mirror box farther aft of the pivot point as the scope is oriented more horizontal, increasing the bal-

ance and stability of the scope for those who insist on capturing first light of an object just as it comes over the horizon.

The Mirror Cell And PLOPing As part of a complete design process, NMT has done their own mirror-cell

Mirror Box The 16-inch mirror box is described on the NMT website as “low profile.” This is most definitely not meant to infer that some compromise has been made in the interest of size or portability. A near necessity of the collapsible truss design NMT employs is an accessible surface area at the top of the mirror box to stably place the secondary cage/truss assembly before handscrewing the truss bases into place. This is one design point that may keep the mirror box in NMT designs from being reduced to super low-profile scaffolding-like mirror box designs without serious consideration of how to combine the positioning of the secondary cage/truss assembly with protection of the primary mirror during assembly. The current box design provides four corners with ample room to place, then fiddle slightly as needed with, the truss bases (Image 2).

The woodwork of the mirror and rocker boxes is completed with a matte black finish on all inner surfaces and two Astronomy TECHNOLOGY TODAY

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THE 16-INCH F/4.5 COLLAPSIBLE-TRUSS DOBSONIAN FROM NEW MOON TELESCOPES

Image 7 - Interior view of the mirror cell and mirror supports, bound- Image 8 - Secondary cage, showing the MoonLite dual-speed focuser, NMT plaque, and added finder scope. ary layer fans, and interior matte black finish.

Image 9 - Optional secondary-heater switch, with 9V battery hidden in Image 10 - View of the inside of the secondary cage, showing collimating thumb screws and Kydex lining. the Telrad.

analysis using David Lewis’ PLOP program. As stated on the davidlewistoronto.com/plop/ website, “It shows how to build mirror cells that outperform the conventional ones, by using CAD to optimize the cell design. As a result, it is possible to reduce the wavefront error by as much as 50 percent compared to a conventional design, or to support a mirror up to about 20 percent larger than typically thought possible.”

The NMT 16-inch mirror cell is built completely in-house featuring an 18-contact floating point design with a steel sling that adjusts on two linear bearings where attached (Image 4). The only restriction on the mirror is gravity – it floats otherwise

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unrestricted in the cell (Image 5). The adjustable sling is positioned at the center-ofgravity along the edge of the mirror so there will never be astigmatism visible in the eyepiece when viewing at low altitudes (which is, again, made easier by the crescent bearings and excellent scope balance).

Finishing Touches A cursory Google search on “boundary layer fans” reveals that, among the involved discussions, there is no doubt of their benefit. Detailed analyses now seem to focus on “pushing air” or “pulling air” as the method to best remove the thin parabolic pool of warm air from the primary.

For the 16-inch Dob, NMT employs

three fans in a “push” (air into the mirror cell) direction to promote mirror cooling and air circulation (Image 6 and Image 7).

The nice touch here to the fan selection is the inclusion of a potentiometer as standard on all NMT scopes, allowing one to give the mirror “full blast” while the sun sets and then to dial the fan speed down to levels that keep the air flowing but allow for stable viewing.

In my own case, I generally keep the fans on at their lowest speed throughout an observing session – any slight vibration from the fans or waste heat from the potentiometer is negligible compared to the lost crispness of a globular cluster as the primary pools another pocket of warm air.

THE 16-INCH F/4.5 COLLAPSIBLE-TRUSS DOBSONIAN FROM NEW MOON TELESCOPES When and how much to use the fans is ultimately up to the observer to decide based on weather conditions, transparency, and the time between setup and first object, but having all the shades of grey between on and off does improve ones odds of finding that perfect combination for such a big scope (and I would urge others limited to on/off switches to place a potentiometer between their battery and fans to see for themselves the difference).

Hooks for counterweights are included as finishing touches on the mirror box for those with extra-heavy eyepiece tastes. My test of smooth motion and balance was performed using a Tele Vue 26-mm Nagler with a 2x Tele Vue Barlow (because the best should be tested with the best). Even at just-off horizontal and with no additional counterweights, the 16-inch scope doesn’t budge.

Secondary Cage One finds that the secondary cage serves one additional function beyond the obvious placement of the secondary cage above the primary.

The secondary cage (Image 8) becomes a constraint for the collapsible truss assembly that separates the truss mounts perfectly for the mirror box – the truss cannot collapse in on itself due to its anchoring by the secondary cage and the truss mounts do not separate beyond the positions of the finger screws on the mirror box.

Furthermore, the secondary cage/truss assembly is stable enough that it can rest on a flat surface by itself, making its own assembly easy with a little practice. NMT recommends this secondary cage/truss assembly-first procedure for 18-inch and larger scopes because the assembly then requires no ladders to complete. I think it an excellent way to put the 16-inch together as well.

The woodwork on the secondary cage is just as meticulous as on the mirror box, complete with Kydex lining and a mounted Telrad that doubles as a battery holder for the optional secondary heater (one of the real nice touches on the scope that efficiently uses free space in the components

Image 11 - The secondary cage/truss assembly and mirror/rocker box in the middle of a secondary/truss-first assembly. The lightweight secondary/truss assembly is picked up, oriented, and placed on top of the mirror box.

and keeps one from running power up the trusses (Image 9).

Secondary Cage Hardware The standard complement of the secondary cage includes an AstroSystems spider with tool-less collimation via knurled thumb screws (Image 10), Telrad, Antares Optics 1/20th-wave secondary mirror (from nearby Rochester, NY), and MoonLite dual-speed focuser.

The secondary mirror and MoonLite selection are again examples of NMT’s decision to incorporate high-end components as part of the design and not to skimp anywhere in the scope. In the case of the MoonLite focuser, its smooth action is all the more obvious when tested against most any other focuser at a Dob gathering. They are simply exceptional focusers.

Collapsible Truss Design The truss discussions at the NEAF booth fell into three categories: (1) That’s a great idea! (2) I thought about that but never tried it. (3) I did something kinda

like it, but I like how you did (something) better. Bringing the collapsible truss design to fruition is NMT and Ryan’s real novel contribution back to the larger Dobsonian community, a point made clear by long discussions of his design and production details at the NEAF booth.

The benefits of the collapsible truss design as implemented by NMT are manifold. The truss assembly itself screws into the secondary cage and mirror box as a single unit of equal-length truss rods: (a) All four mount positions are identical; (b) There is no variation in the lengths of certain trusses due to variations in the way separate-pole trusses are placed into split blocks (or similar designs). The secondary cage/mirror box separation is always the same at all connection points every time.

The result is an assembly that requires little collimation. The collapsible truss design also allows one to set up the scope in the reverse manner of a separate-truss design (Image 11).

Here, the secondary cage can be assembled on top of the flared-open truss first

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THE 16-INCH F/4.5 COLLAPSIBLE-TRUSS DOBSONIAN FROM NEW MOON TELESCOPES

Image 12 - View of the secondary cage thumb-screw mounting and Image 13 - This scope is “Lightholder-equipped” (linear bearing also shown at upper-left). top of the collapsible truss.

at a comfortable height for most observers.

The secondary cage then acts as a restraint on the truss flexibility, allowing one to pick up the entire secondary-cage/truss assembly, place it over the screws on the mirror box, then let the whole truss rest stably on the mirror box as you tighten the finger screws at each position.

The disassembly works in the exact reverse, allowing one to close up the mirror box (and cover the mirror) before disassembling the secondary cage from the trusses. Again, this is the recommended procedure for the 18-inch and larger scopes, but I find it just as practical for the 16-inch. The trusses themselves are aluminum, powder-coated to a matte black (for wear resistance and to further darken what the shroud already covers), and with no sharp edges, while the connectors are all extra-large finger screws for those frosty 2 a.m. “I can’t feel a thing” disassembly sprints (Image 12).

The result is a scope that can go from separate components to ready-andshrouded-for-observing in under two minutes (as demonstrated in the Youtube videos).

Lightholder-Equipped I had no doubt about the quality of the woodwork and components Ryan selected for NMT #1, which made it easy for me to choose to buy the absolute best mirror I could find for my only-once Dob. Just as I have seen many an amateur astronomer

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start with seemingly decent eyepieces, then eventually sell and buy their way up to Tele Vue (my personal bias, anyway), I have heard too many stories of observers with primary mirrors that eventually have their faults found out over the course of many observing sessions (the primary mirrors, that is). The solution, while not cheap, is simple – start with the best you can get and never, ever, find yourself regretting an “intermediate” purchase when you go to finally take the plunge on a high-quality primary.

From the short list of primary mirror vendors Ryan originally recommended, I went with a 12.5-inch F/4.89 Lightholder because the price of the mirror for its quality was quite competitive with other highend vendors (and, frankly, John Lightholder is as meticulous with his testing and provided paperwork as he is a real fun guy to exchange emails with). The mirror alone cost more than many of the major vendors are currently charging for complete-and-shipped 12-inch Dobsonian telescopes. The reason is simple – it is absolutely worth it.

The first group outing/observing gauntlet of NMT #1 at Darling Hill Observatory in Tully, NY was a complete jaw-dropper, with the 12.5-inch mirror and Antares Optics secondary outperforming other 16-inch scopes in terms of image clarify, definition, and overall brightness.

NMT’s 16-inch f/4.5 Dob is, simply,

that much better than the 12.5-inch, gathering 80 percent more light on a still perfectly figured mirror (Image 13). To have the spiral arms in M81 stand out, to see Stephan’s Quintet without need of averted vision, to see planetary nebula take on richer colors and to have their central star visible, and to pick out the occasional globular cluster in the Andromeda Galaxy on a transparent CNY night all thoroughly convince one that the only rational corners one should cut in the purchase of a 16-inch Dob are those of the box joints.

That said, NMT allows the customer to select their mirrors or use their own in rebuilds. As a general endorsement of Lightholder mirrors, I cannot say enough about just how good Lightholder primaries are, and I am very pleased to know that Ryan opted to complement his expert woodworking skills with premium optics to produce a truly remarkable NMT product.

Closing Thoughts When considering the quality of the build and the choice of components, I would have no hesitation in recommending that the dedicated amateur astronomer and other only-once purchasers like myself consider the New Moon Telescope 16-inch f/4.5 Dob as their lifetime gateway to the Nighttime Sky. Fellow amateur astronomers will appreciate not needing (or wanting) to bring their scopes to your observing sessions.

ASTRONOMY

TECHNOLOGY TODAY Your Complete Guide to Astronomical Equipment

LOOKING BACK SERIES - Vol. 8 -

2014 Issue 4

THE GONDWANA TELESCOPES MARANA A Big-Aperture Cure for Fat Lips and Slip Discs Our second dobcentric article by Sean Melehan was submitted to us all the way from Australia and features another custom Dobsonian builder, Alexander Massey, and his beautifully crafted Gondwana Telescopes.

76 Astronomy TECHNOLOGY TODAY

The Gondwana Telescopes

Marana

A Big-Aperture Cure for Fat Lips and Slip Discs

By Sean Melehan

Image 1 - The Marana’s integrated 40 cm by 61.5 cm by 20 cm finely crafted box is enclosed in its included swag with its 11mm diameter truss poles stored in their custom-tailored carry bag.

Less is more.

I ponder this old chestnut of wisdom as I survey my slowly swelling mouth in the mirror. There are two distinct divots in my fattening, bloodied top lip – courtesy of my front teeth – and while shielded from view by an equally expanding bottom lip, the salty taste of blood tells me there is more damage out of sight.

I valiantly wonder if the throbbing sensation is going to affect my averted vision later in the night.

What has the poor state of my face got to do with new Australian company Gondwana Telescopes and their line of travel telescopes?

Image 2 - The Marana with its box enclose unfurled from the swag and truss poles removed from their carry bag.

Well, the thing is I gave myself a double fat lip by trying to wrestle my 16-inch rolled-steel truss Dobsonian out from the under the stairs. A growing family has pushed my scope space gradually into the confines under the stairs; optics are precious, especially big ones, and I just refuse to store my scope in the garage for fear of dust – and two crazed cats who are liable to do anything, particularly exceedingly expensive anythings.

This damage was done getting the rocker box out and, while I subsequently wrestled the LTA out successfully, bloodied lips and all, I couldn’t help but wonder what havoc I may one day wreak getting

Image 3 - The components of the Marana revealed and ready for assembly. Everything stays safely put when the case is closed.

the truly heavy mirror-bearing bit of my astronomy gear out of the house.

Unless ... I lighten things up!

I must confess – I have always been a fan of a good, solid scope. I can’t tell you why, exactly: after all, I almost slipped a disc as a 16-year-old when I used to wrestle a cardboard-tube Meade DS-16 onto an equatorial mount in the late 1980s.

Fortunately, my poor father was always roped into the process (sorry about the hernia, dad!), but the views of M104 (albeit swimming in a circle of seagull stars) was always worth it.

Astronomy TECHNOLOGY TODAY

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THE GONDWANA TELESCOPES MARANA Solid equals stable, right? Protected optics. Rock solid mounts. Views that sit where you put them, and images that donâ&#x20AC;&#x2122;t shiver in the eyepiece like a kid at his first late-night horror flick.

Image 4 - The integrated box enclosure contains no weight-reducing holes, trading sealed protection of the enclosed optical components over the modest weight advantage of perforations. Note the custom plywood knobs â&#x20AC;&#x201C; big enough for comfort, yet lightweight.

Well, maybe not.

In this era of everything electronic and otherwise that opens and shuts on a Dobsonian â&#x20AC;&#x201C; plus enough mirror fans to lift them into higher orbit than the Hubble Telescope â&#x20AC;&#x201C; sometimes the simple premise behind the design gets lost.

Balance it well so it works. Give your optics a chance to perform without the hindrance of their constraints. It really isnâ&#x20AC;&#x2122;t rocket science (although, granted, you are pointed at the heavens).

The term travel scope may well apply to pretty much any telescope that isnâ&#x20AC;&#x2122;t nestled comfortably in an observatory, or has wheels and stays set up in storage. By sheer virtue of increasing light pollution and our pursuit of suitably dark skies, it is a case of have scope, will travel.

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2014

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2013 Star Products

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THE GONDWANA TELESCOPES MARANA

Image 5 - Marana UTA details.

Gondwana Scopes founder and scope builder Alexander Massey dropped the 12-inch Marana for me to review one rainy Sunday afternoon on his way back from the annual Ice in Space Astro Camp

in a sleepy little rural spot called Lostock in NSW, Australia.

As fellow artists at the eyepiece, it was a good chance to have a yarn and compare some sketches – it’s the only way to really

see what goes into an astro sketch, and we both agreed that it is a dying art that transcends photography in showing exactly what can be seen by amateur observers.

Being an artist of note, it was no surprise that Alex would deliver a scope that looks like a real piece of art. Seeing the Marana – an Aboriginal word meaning ‘stars’ – assembled really does get you wondering if it is form that follows function, or the other way around. Like everything else in this world, passion for a pursuit really does shine through when it comes to creating.

This scope arrives in two parts: a nicely crafted box (the one I reviewed was wrapped in the optional swag) and a tailor-made bag containing the poles (Images 1, 2 and 3).

The box contains no weight-reducing holes (Image 4); the design here is for a travel scope and, at least in Australia, getting to dark skies often involves dodgy bush roads full of potholes big enough to

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Astronomy TECHNOLOGY TODAY

THE GONDWANA TELESCOPES MARANA swallow a small car and ruts that may draw a morning-light search party.

Bouncing cars often bring unwanted flying bits that can easily sail into such a box and mess with the optics. You want to be able to pack without fear of damaging your scope!

So no holes.

And I can’t say they were necessary, as the travel box was easily light enough to pick up by the handles and not only put it in and out of a car, but carry it up a winding staircase to take in a northerly view of Mars from my top deck at home.

The Marana design also lends itself to be ‘carried’ by components, rather than just as one 21-kilogram (46.3-pound) piece, should weight be a consideration. The single heaviest component is the mirror box at 10.5 kilograms (23.1 pounds).

Unclipping the travel case reveals the well-packed contents that stay put regardless of travel motion (Image 3).

The removable secondary clips tightly into its small niche within the box; a small built-in compartment stores all the necessary fasteners and hardware needed to get you in business.

Putting the Marana together isn’t hard at all. Alex gave me some verbal instruction and a single demonstration.

My first attempt took about 20 minutes as I was taking my time. This fell to around the 15-minute mark after a few goes, and I reckon after six months of use you’d be putting it up under 10 minutes – not that it’s a race ... but clouds and optimum viewing conditions can be awfully pushy customers at times.

Poles bolt in to the LTA, then bolt onto the UTA. Side bearings bolt onto the side of the LTA and the brace similarly bolts in, all with handmade bolts capped with nicely finished plywood knobs (Image 4). The pivot bolt drops into the mount, which slots onto the base. Like I said, not complex. Drop the secondary into place – the magnet and guiding components clip it firmly in place – then slide the red-dot finder into position, strap the shrouds (one each for top and bottom into position) and you’re almost ready. Four Teflon-coated guides screw into position to keep the tube assembly from wandering out of position on the mount.

For collimation, there are thumb screws on the secondary which are always a snap to use (Image 5). The primary is collimated using a handmade device that clips over the collimating bolt heads (Image 6). It’s another handmade touch that makes good, simple

Image 6 - The Marana includes a handmade device that clips over the three collimating bolt heads for ease of primary collimation. This feature results in an exceptionally compact assembly.

sense. One subtle design aspect of the collimation system is it also reduces the overall volume of the mirror box, and makes for a more compact stowed scope.

This Dob is quite clever like this in quite a few elements of design.

Astronomy TECHNOLOGY TODAY

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THE GONDWANA TELESCOPES MARANA So the Marana is together. The tube assembly is so light you can pick it up with little effort with one hand, using the other hand to balance and guide it into position.

Image 7 - The 11-mm carbon-fibre truss pole ends are tipped with metal for protection. The focuser board holds the 2-inch KineOptics HC-2 helical focuser firmly in place, with no detectible flexure.

Impressions?

What strikes you about this Dob – apart from the feel of a handcrafted instrument built by someone with an acute understanding of the craft – is twofold: the bearings are big; and it is quite unusual in that the struts bow out (see caption image).

The bearings are a whopping 60 cm – that’s a whopping 24 inches. That’s as big as you get for a lot of premium 18-inch scopes

these days, and this is a 12inch scope.

As will be discussed, this means counterweights don’t get much of a say in the performance of this scope. It also means a lightweight scope, far from feeling flimsy, is as solid as a rock.

As for the struts: at just 11 mm wide, they are surprisingly small, but their loaded design means they work against each other to provide stability. It is unidirectional carbon fibre, tipped with metal for protection (Image 7). At 11 mm in diameter, they allow for smaller and lighter clamps, yet the engineering that forces them to work against each other produces

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THE GONDWANA TELESCOPES MARANA remarkable rigidity and strength. Travel scopes have been known in the past for not holding collimation. I can report that the Marana does pretty well here.

From dead horizontal to straight up vertical, laser collimation slips just off the centre of the doughnut to the inside edge of the doughnut. This is with a very precise Howie Glatter collimator – and a 2inch version at that, which, as far as laser collimators go, is about as meaty as they get. And it holds that collimation for at least a good two-hour session of observing.

Now here’s the thing: I collimate my scopes at roughly a 45-degree angle, and not dead flat. I don’t know about you, but it’s a rare night when I have my scope remotely pointed at the horizon: there’s usually something in the way, and even if there isn’t, the seeing down low is like looking through the bottom of a schooner glass. You only do it for the novelty value – at my latitude, that includes picking off the Andromeda Galaxy or Whirlpool Galaxy as they pop up briefly over the horizon. If a scope can hold its own from about 25 degrees or so to 90 then I’m as happy as a pig in mud.

The version I had was not set up for Argo Navis, but this is readily available as an option (and Marana comes ready with encoder couplings) – of course, they’re both Aussie products after all. I don’t feel the absence of digital setting circles affected the review at all and think it in fact kept the attention squarely on the scope itself.

The Marana is offered either with Skywatcher Optics, a customer’s sourced set of optics, or donor optics from an existing telescope.

This version was equipped with Skywatcher optics, and while the test was not one of optics, they threw up a pretty sharp, scatter-free image. Part of that result comes down to the fact that the optics were allowed to perform; so it was a clear case of mission accomplished.

There are no fans on this scope. Alex

likes to point out that you cannot force Pyrex to evenly cool faster than it wants to, and blowing a fan in the centre of a big mirror does nothing but create a cool constricted centre, a warmer expanded ring ... and a bad image. As he points out, the massive professional observatory scopes are not built by astronomers, but by engineers, whose expertise does not lie in observing the stars but rather in the thermal properties of materials used in the construction of a scientific instrument.

The six-point flotation cell utilises disc springs that are robust, strong and laterally stable, as opposed to compressional coil springs that tend to float about as they buckle with each twist of a collimation screw. The mirror stays exactly where you position it.

Eyepiece height at zenith is 170 cm (66.9 inches), and the scope unfurls itself from a box just 40 cm (15.75 inch) deep, 61.5 cm (24.2 inch) wide and 20 cm (7.9 inch) tall.

pieces without having to screw and unscrew filters all night. It also means you can use 2-inch filters with your 1.25inch eyepieces.

And for its overall 21 kilograms (46.3 pounds) of weight, the way the Marana dealt with big eyepiece glass was amazing. A 13-mm Ethos? No counterweight required at all. Throw on a Paracorr 2 as well and this scope was sitting pretty with a tiny 1-kilogram (2.2pound) counterweight that clipped on the back of the LTA. The single counterweight dealt with a 21-mm Ethos with no problems.

While I didn’t have a second counterweight handy, I am sure it would cope with the addition of the Paracorr just fine. The specially designed counter weight system was adopted by Alex on his observation that rip-cords, braking systems and clutches, only serve to change the action of a scope, and a lightweight instrument deals poorly with such hindrances.

So I’m out under the starry skies. What strikes me the most, straight up?

Given my penchant for heavy, robust scopes, I was really impressed that such a light scope could be so sure footed. It doesn’t feel flimsy. Its movements are smooth as silk but solid. Like a well-balanced Dob should, it moved obediently with the push of a single finger, and stopped exactly on queue.

Nudge tracking was as easy as it gets.

Despite the light weight, a nudge moved the image, which then stayed put. No shimmying and shaking. It actually felt like my big rolled-steel Dob, only smoother and more precise. It really was quite unexpected.

The focuser board held the eyepieces in place, with no discernible flex evident for the one-side mount. The focuser is a 2-inch KineOptics HC-2 helical (Image 7) which also facilitates 2-inch filters with a specially designed threaded drawtube that means you can switch eye-

So were there any quibbles?

Only very minor ones, really. I’d like to see a bit of blackening on the primary mirror clips, as I’m a bit obsessive-compulsive about stray light, and at least in my suburban location, I would be keen to see a full top-to-bottom shroud. The metal clamps to attach the UTA are polished – these may show less wear and tear over time with a flat finish, as there is a bit of technique involved with loading the poles into position. But like I said, these are minor points indeed and simple to address.

But all in all ...

Gondwana is offering a bigger version. Like 16 inches. Even if I’m only travelling out from under the stairs, it is well worth considering. I earned my stripes with the heavyweight DS-16 of yesteryear. I’ve seen the light, so to speak.

After all, fat lips sting like blazes in the cold night air!

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