Professor Newman on...Focus stacking

Professor Newman examines a technique to overcome limited depth-of-field in close-up shooting

Depth of field is a big limitation in many types of photography. The problem is that optical means of extending depth of field inevitably suffer from a quality penalty.

This penalty is twofold. Firstly, stopping the lens down to provide additional depth of field reduces image sharpness due to diffraction. This is inevitable. I have seen statements on the internet claiming that diffraction blur is dependent on the lens, or that it can be avoided by using cameras with ‘large pixels’. Both of these ideas are myths. The effect of diffraction is a fundamental limitation. If we consider the case of an image reproduced to a given size, the effect of diffraction depends on the size of the aperture, not the f-number. As a consequence, diffraction is firmly linked to depth of field – the more depth of field, the more blur it causes. So the notion that smaller sensors offer more depth of field does not offer a way out of this particular bind.