Archived posting to the Leica Users Group, 2003/05/07
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]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. > > At 09:06 AM 5/7/2003 -0700, Jerry Lehrer wrote: > > >Don > > > >In this regard, I wish that someone could explain why and HOW > >different lenses with the same aperture and focal length can produce > >different depths of focus. How can the laws of optics be ignored? > > > >Get as technical as you need to. I can handle it, but don't resort to > >mysticism, please. > > > >Jerry > > -- > To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html - -- To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html