Depth of Field vs Focal Length, 12th December 2006
We set out to test Mike Dodd's hypothesis that depth of field was independant of focal length. We carried out two sets of tests, one moving the camera to keep the subject the same size in the frame, then changing the focal length. Secondly, keeping the camera and subject fixed and then varying the focal length. Different apertures were used for each test. The direct-from-camera JPGs are available from the 'large' version of each image.
These are two montages from the second test, with the aperture on f2.8 and the focal length at 200mm then 70mm. Sadly I forgot to bring a remote release for the camera, so had to up the ISO to 800 to get a reasonably fast shutter speed - this has dropped the image quality and made comparison more difficult, but to my eye at least, the depth of field appears to be greater in the second part of each image.