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 The focal length of the lens The wider the angle (in other words, the shorter the focal length), the greater the depth of field. A 20mm lens has much greater depth of field than a 200mm.

 The distance to the point of focus Depth of field is greater when you’re focused on more distant objects. In real close-up work depth of field is minuscule.

We might assume that an aperture of f/16 or even f/22 would be best. However, due to diffraction, overall sharpness tends to fall off at the smallest apertures. The best compromise between depth of field and sharpest results is often with the lens roughly half way open (eg at f/11 for a lens whose minimum aperture is f/22). At lower ISO ratings this means a slow shutter speed, which in turn means using a tripod or risking camera-shake. Today we have both image stabilisation and the option to turn up the ISO a few notches.

The difference in depth of field is caused by changing the aperture from f/4 to f/8 (Chiz)

Making the most of depth of field

Remember that depth of field extends both behind and in front of the principal point of focus. If you focus on the most distant object in a scene, although depth of field is theoretically greatest, you’re only using half of its potential. The fact that more distant objects would be in focus – if there were any – is immaterial. In a typical landscape shot, the most distant part of the scene will be a skyline or horizon. Focusing on this is, as near as makes no difference, focusing on ‘infinity’. (Infinity has a somewhat specialised meaning in optics.) Depth of field theoretically extends beyond infinity, but this isn’t much use to anyone except Buzz Lightyear.