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Image: Chris Rutter

The Manual on Manual

key concept Make sense of manual Manual exposure sounds complex, but it’s actually rather simple ■ Your Nikon D-SLR uses three key exposure settings: shutter speed, lens aperture and ISO (sensitivity), and the settings have been designed in a very clever way – you can balance one against another. If you want to use a faster shutter speed, you can increase the lens aperture setting. This allows more light through to compensate for the shorter exposure. Alternatively, if the light is too dim for the shutter speed you want to use, and you’re already using the lens’s maximum aperture, you can increase the ISO setting to compensate for the dimmer light.

Shutter speed

Lens aperture

1 sec

f/5.6

2 secs

f/8

4 secs

f/16

8 secs

f/22

An exposure of eight seconds at an aperture of f/22 was used to blur the water in this picture, but this was only one of a number of possible shutter speed and aperture combinations for the same exposure – others are shown above.

1 Shutter speed The shutter speed controls how long the shutter stays open – the length of the exposure. Exposures are cumulative. If you double the time the shutter stays open, you double the exposure.

2 Lens aperture The aperture is an adjustable diaphragm inside the lens which changes the amount of light passing through. If you double the size of the aperture, you double the amount of light and double the exposure.

3 ISO (sensitivity) You can also increase the camera’s sensitivity to light. This method of increasing the exposure is not ideal because it increases the digital noise in the image, but it can be useful in poor light.

when to lock down The exposure

There are times when you don’t want the exposure to change…

IMAGE ANALYSIS 1 If you use a graduated filter to darken the sky, working out the exposure manually is simpler 2 You can check the exposure in different parts of the scene to decide on the best settings 3 Using a small lens aperture has allowed a long exposure time (shutter speed) to blur the water

Landscape photographers also like to blur moving water with a long exposure, which often means using an ND filter. These are evenly dark all over. You need to measure the exposure without the filter, add the filter and then apply a fixed correction. You have to do this in manual mode, because the filter will be too strong for the camera’s light meter to get an automatic reading once it’s fitted. Finally, most landscapes need maximum depth of field, or near-to-far sharpness, which means using a small lens aperture. In manual mode it’s easy – you simply balance the smaller aperture with a longer exposure.

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■ This panoramic image was created by stitching together a series of overlapping images. For this process to work it’s essential that the exposure doesn’t change, even if the lighting varies across the frames.

■ This HDR (high dynamic range) photo is a composite of three different exposures. For this to be effective, they have to be controlled manually, with precise exposure differences between each one.

August 2014

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