Archived posting to the Leica Users Group, 2003/05/07
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Jerry, Why would I rebut that? I only rebut things that are wrong ;-) And, the issue of depth of field vs depth of focus, Jim and I have discussed at some length, and we both see eye to eye on this issue. Austin > Jim > > I'll buy that! Sounds reasonable to me. > > Now I'm waiting for Austin to rebut that! :-) > > Jerry > > Jim Brick wrote: > > > All 90mm lenses, basically, produce the identical depth of field. If one > > 90mm lens has more contrast and higher resolution numbers, and > the ability > > of recording fine detail better than the others, it will > "appear" to have > > LESS DOF than the other lenses. This is because of the visual sharpness > > difference between the sharp and unsharp areas. There is an > abrupt change > > between the very sharp and the less sharp areas. This is also why lens > > manufacturers say that to fully utilize the DOF scales on modern lenses, > > use it as if you were shooting two stops wider, ie; shoot at > f/16, read the > > scale for f/8. The scales were computed back when lenses were > not so sharp > > and film was not nearly as good as today's lenses and film. > > > > If your lens exhibits lower contrast, less fine detail > recorded, etc, then > > the difference between the sharp and unsharp areas is less apparent thus > > giving the "impression" of greater DOF. It is a smoother > transition between > > the sharp image parts and the less sharp image parts. > > > > This is a very well known fact and is why many people think > that old lenses > > have greater DOF than new lenses. It's not true, it's simply the visual > > difference (sharpness contrast) between the sharp and unsharp areas. > > > > Jim > > > > PS... Depth Of Field is what you see in the photograph. Depth > Of Focus is > > at the film plane and, even though (like depth of field) is > dependent upon > > the aperture, is a different subject. - -- To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html