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EXPOSURE Aperture-Shutter Speed-Iso Photography is the art of recording light. In order to record light you need to know how to tell your camera how much light to record. Understanding photography exposure allows you to give correct instructions to your camera.

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Shutter Speed Shutter speed, also known as “exposure time”, stands for the length of time a camera shutter is open to expose light into the camera sensor.

In a camera, the shutter blocks all light from entering the camera UNTIL you press the button. Then it quickly opens and closes, exposing the sensor to a brief flash of light. You can control the length of time the shutter remains open by setting the SHUTTER SPEED. If the shutter speed is fast, it can help to freeze action completely, as seen in the above photo. If the shutter speed is slow, it can create an effect called “motion blur”, where moving objects appear blurred along the direction of the motion. The longer your shutter is open, the more light enters the camera. Your photo will become over exposed if you slow the shutter speed without adjusting your aperture or ISO

Shutter speeds are typically measured in fractions of a second, when they are under a second. For example 1/4 means a quarter of a second, while 1/250 means one two-hundred-and-fiftieth of a second or four milliseconds. If you want no blur – maximum sharpness – you set very short exposure times. If you want blur, set longer exposure times and stabilize the camera by setting it down, using a tripod, or bracing against something to steady the shot. • • •

1/60 – 1/30sec is good for fast-moving action. 1/30 – 1/8 sec is cool for people walking in crowds, for blurring water in fountains etc. and is just about hand-holdable. 1/4 – 4 sec is a good start for short streaks of car lights at night.

Your camera may have a “shutter priority mode”. In shutter priority AE you set the shutter setting, and the camera figures out the right aperture setting for the right exposure. You may choose to use shutter priority AE when your priority is control over motion blur.

One of the key factors to understanding photography in general and shutter speed in particular is practice, trial and error, so go out and take some shots. Try something different every time. Try long exposures, short exposures, moving objects, night photography. Then go back home and analyze your pictures. Is a picture blurry? Is it sharp? Does it show motion? Action? The more you will ask yourself those questions, the better grasp you will have over the shutter speed control.

A fast shutter speed will require a larger aperture to ensure sufficient light exposure, and a slow shutter speed will require a smaller aperture to avoid excessive exposure.

f/1.4 is larger than f/2.0 and much larger than f/8.0 Above: Diagram of decreasing aperture sizes (increasing f-numbers) Below: A lens shown with two different apertures:


Aperture refers to the diameter of the hole through which light travels to the camera’s sensor. To understand aperture, think about the human eye. When we walk into a dark room or outside into the bright sunlight, it takes a moment for our eyes to “adjust”. The pupil (the black part) of our eyes either expands or shrinks, controlling the amount of light passing further into the eye. The amount of light that enters the retina (which works just like the camera sensor), is limited to the size of the pupil – the larger the pupil, the more light enters the retina. The pupil is essentially what we refer to as aperture in photography.

In photography, aperture is expressed in fnumbers (for example f/5.6). These f-numbers that are known as “f-stops” are a way of describing the size of the aperture, or how open or closed the aperture is. A smaller f-stop means a larger aperture, while a larger f-stop means a smaller aperture.This can be confusing since we are used to having larger numbers represent larger values. Aperture priority is a semi-automatic shooting mode used in cameras. It allows the photographer to choose an aperture setting and allow the camera to decide the shutter speed and sometimes Iso for the correct exposure.

The size of the aperture has a direct impact on

depth of field

the , which is the area of the image that appears sharp. A large f-number such as f/32, (which means a smaller aperture) will bring all foreground and background objects in focus, while a small fnumber such as f/1.4 will isolate the foreground from the background by making the foreground objects sharp and the background blurry.


Above: Flowers shot with a small Aperture (large f/stop number) Below: Smaller depth of field created by using a larger aperture (small f/ stop number)

is the level of sensitivity of your

camera to available light. The lower the ISO number, the less sensitive it is to the light, while a higher ISO number increases the sensitivity of your camera. The component within your camera that can change sensitivity is called “image sensor” or simply “sensor”. It is the most important (and most expensive) part of a camera and it is responsible for gathering light and transforming it into an image. With increased sensitivity, your camera sensor can capture images in low-light environments without having to use a flash. But higher sensitivity comes at an expense – it adds grain or “noise” to the pictures.


exposure lesson for photo class

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