monty rakusen wrote:
I've done my testing and found it is focussing at the right plane and tested all
the apertures and found it only good up to f16
Monty:
We've been using the Rodenstock digital lenses for four years now, and have done some testing concerning sharpness. While we don't usually use these lenses for macro work, I think you may be fighting a different problem that optical sharpness.
A few years ago there were a couple of white papers floating around concerning optimum apertures for digital photography. While I can't cite technical or statistical facts concerning diffusion etc., the gist of the information came down to the rule of thumb that the best corrected optics will be sharpest at an aperture that is closest to the well size in microns. That means that if you're shooting with a philips chip with 12 micron well sites, f11 is probably going to be the optimum aperture for sharpness, with the 11mb chip, the 9 micron well site means optimum aperture will be f8 or so. Stopping down actually decreased apparent sharpness of the unsharpened files. Chips do not record light falling on them the same way film does (did?).
Our tests confirmed this phenomenon, but judicious use of USM offsets the problem for most of what we normally shoot, and we now generally avoid even attempting to shoot below f22. It hasn't been a problem so far, but again we rarely shoot macros. On those occasions when we've needed closeups, we've actually shot multiples at various focuses (foci? focusi?) and layered the files. There is a software solution that was alluded to on this forum several weeks ago that addresses this problem.
With the well/site size of some of the newer cmos dslr's out there getting really small (I think I've seen 4 and 5 microns for well sizes on some of the newer chips), I'm thinking that there's a lot of sharpening going on in the onboard processors.
-- Jeff Smith
Smith/Walker Design and Photography
P. O. Box 58630 Seattle, WA 98138 ph: 253-872-2111 fx: 253-872-21400
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