I guess I should mention that The letters "DL" placed upon lenses by the
advertising department seldom, if ever, means the lens is diffraction limited.
If they were taken to court about it they would probably say it means DeLuxe.
--
graywolf wrote:
Actually it is both. Diffraction is based upon the diameter of the
aperture diameter and the dispersion angle of the light rays which is
affected by focal length. So the shorter the lens, and the smaller the
aperture, the worse the diffraction.
The lens will be best at the widest f-stop that is fully corrected. If
that is also the maximum f-stop on the lens the lens is said to be
diffraction limited (DL). There were actually quite a few DL lenses with
maximum f-stops of f8.0 or so. I know of only one that was supposed to
be DL at f2.0, the French made 100mm/2 Kinoptik (I suppose there may
have been others that I have never heard of).
--
graywolf
http://graywolfphoto.com/graywolf.html
