How to use your Camera to shot good Pictures/Photo (Depth of field preview)

Apart from the shutter release, film winder, focusing and exposure controls, even the simplest cameras have a few additional knobs and switches that are either safety devices or provide an extra degree of control. Used correctly they may not only make picture taking more reliable but can also increase the versatility of the camera.

Here’s how to use the extras most commonly found on modern cameras, and in some cases what you can do if your own camera lacks them.

Depth of field preview

Many cameras have a fully automatic aperture diaphragm which allows the user to focus and take exposure readings at the lens’s widest aperture setting. When the shutter is released the aperture automatically stops down to whatever has been set on the aperture ring.

A depth of field preview button or lever closes down the lens to the taking aperture without disturbing the settings you have previously made. This is usually only found on a single lens reflex camera and allows you to study the range of sharp focus through the viewfinder before making an exposure. The facility does have limitations however, because using it causes the viewfinder to appear much darker, and at very small apertures (f22 for example) it may be difficult to see the image. When photographing a face, most people focus on the eyes. At fairly close distances the ears and tip of the nose may be out of focus. Using a depth of field preview allows you to check if this is happening and lets you know if you should select a smaller aperture to increase the depth of field. Conversely, you may wish to separate the main subject from a confusing or distracting background by using a wide aperture. It is possible that, although you have selected a fairly wide aperture to complement a particular shutter speed, there may still be sufficient background sharpness to spoil the picture and detract from the three- dimensional effect. Check this with the depth of field preview, and open up a stop or so if necessary.

Manual and pre-set diaphragm lenses allow you to close the aperture manually and watch the way more of the subject becomes progressively sharper as the aperture becomes smaller. Fully automatic diaphragm lenses fitted to cameras with no depth of field preview are not quite so simple to use if you specifically want to determine the exact range of sharp focus.

Nearly all lenses for SLR cameras have a scale of figures additional to aperture and distance scales: these figures run in pairs either side of a central reference mark. This is a depth of field scale which shows the photographer the range of distances in sharp focus.

Once the lens has been focused and the aperture set, look at the two figures on the focusing distance scale which line up with the pair of marks for your set aperture. These are the nearest and farthest subject distances which will be in sharp focus. For example, with a 50mm lens on a 35mm camera set at fl6 and focused at 2 metres, the depth of field extends from 1.5 to 3 metres. Most photographers gain a fairly accurate idea of the depth of field range for particular apertures and focusing distances by experience. However, even the most knowledgeable will need to check depth of field on occasion, particularly in close-up work when the range of sharp focus may be only millimetres.

Using a wide aperture limits depth of field, while a small aperture extends it.

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