View Full Version : optminal aperture for Nikkor W 210mm?

chris jordan
25-Apr-2002, 13:39
Does anyone know with authority what's the sharpest aperture for the Nikkor W 21 0mm? I've always presumed it's f/11, but when i shoot for max sharpness it woul d be nice to know.


Ellis Vener
25-Apr-2002, 13:50
more like in the f/16 to f/22.5 range than f/11. But to be honest I haven't performed any bench tests to prove it.

Jason Greenberg Motamedi
25-Apr-2002, 14:21
This brings up an question about which I am unclear. I know that, at least with my 150mm, the sharpest (accord to my resolution tests) is ~f/11. As the lenses get larger, does the sweet spot move up the scale? A number of my longer lenses will stop down to f/90 (or more in the case of some barrel mounted Apos). Is the defraction greater or the same with a 150mm at f/64 as a 600mm at f/64? or is this a fuction of design? Thanks in advance, and sorry to digress .

chris jordan
25-Apr-2002, 15:22
f/90?? bitchin!!! Edward Weston had a custom-made aperture that would stop down to some incredibly small aperture like f/512. he wasn't technically savvy enough to understand circles of confusion, so he wasn't aware of the fuzziness problem with very small apertures; he just wanted very high depth of field for his pepper photos. notice sometime how fuzzy they are, even as contact prints. but, also notice how it doesn't even matter because they are some of the greatest photographic images ever made...


26-Apr-2002, 00:09
I've been checking aerial image resolutions on my lenses and the results may surprise some people. On axis the sharpest apertures are always wide open for f/9 and slower modern lenses (including Artars), and within a stop of wide open for the f/5.6 variety. Diffraction is a fact of life (physics?) that cannot be overlooked, and it kicks in quickly. I've read 200+ lp/mm for most of my lenses that open to f/5.6, but it quickly goes downhill (F/11 will give 140lp/mm at most). Not having a true optical bench I cannot accurately measure off-axis at the same focal distance because I cannot calibrate to a flat image plane, so I stopped trying to do off-axis measurements (what's the point?). Since the only time "sharpness" is a real issue is with 2-dimensional subjects, it's really just a matter of curiosity to most people. Depth of field and contrast is much more important to the appearence of sharpness in most of our photos. That, along with anomalies in the actual flatness of the image plane, and film flatness/location issues renders the importance of ultimate sharpness as a moot point for most occasions.

26-Apr-2002, 00:12
BTW resolution for my Nikon 90SW is no poorer than my Fuji 600C at f/16 and higher - focal length has nothing to do with diffraction limits.