For a given focal length (wide angle) lens, is the amount of light fall off the same regardless of manufacturer? In other words, is fall off strictly a function of focal length?

-- Mark Windom (mwphoto@nwlink.com), March 23, 2002

Answers

No. The amount of fall-off is dictated by the exit cone of the lens, and this can vary quite a lot with the design. A lens with a longer back focus than its focal length (a retrofocus design) will generally give less fall-off, but there's a limit to what can be done before geometrical distortion of the image becomes a problem. There are other little optical tricks that can be employed by the lens designer too, but light fall-off can never be completely eliminated.

-- Pete Andrews (p.l.andrews@bham.ac.uk), March 25, 2002.