Bob Fowler
Richmond Hill Camera Club

Recently at Photokina in Germany it became apparent that some major camera manufacturers are concentrating on bringing full-frame digital cameras to market at more affordable prices.  Why might you be interested in a ‘full-frame’ (i.e. large sensor-equipped) camera?

Two reasons, mainly:

  1. Generally  larger information advantages of a larger sensor (more and larger pixels with positive consequences for image quality and less noise in low-light situations).
  2. Better control of depth of field.

This time I have concentrated on how the larger sensor helped achieve the second aim, namely how it affected the camera’s depth of field (dof).

All other factors being equal [focal length, distance from subject, and aperture setting (f-stop)] the size of the sensor makes a major difference in the dof possible in an image.

If one uses the full-frame dof as a base, one can calculate the equivalent f-stop effect of the other sensor sizes by multiplying the f-stop  of the chosen camera by its crop factor.  Thus, if your APS-C camera has a crop factor of 1.5 and the full-frame camera’s f-stop is f8, your equivalent f-stop effect will be f11, and if your camera phone’s crop factor is 5.6, your equivalent f-stop effect will be f22, probably its highest possible setting and enough to get from camera to infinity as a dof.  Similarly a 4-thirds style camera would have an equivalent f16 result on its hands. This matters a great deal if you are trying to achieve a narrow depth of field for purposes of portrait photography or just to separate out your subject from distracting background matter.

As the sensor  size decreases, the need to manipulate the other dof factors becomes increasingly necessary and can make the desirable result more difficult to achieve, though to some degree possible.

This forms part, but not the only part by any means, of the decision to spend the extra money for a full-frame digital camera.