PentaxForums.com - View Single Post

Richard Day · 02-10-2008, 04:57 AM

Originally Posted by amateur6

Thanks very much Richard! I'm going to do another round of test shots (actually I just did but I'm still getting a wicked back focus to correct). *sigh*

Of course, the diffraction issue begs the question: can Pentax perhaps take a lesson from the elevator industry and please OVER-engineer instead of UNDER-engineering? In other words, if your f22 has issues, well, you shouldn't really have an f22, should you? Especially true of the 100mm Macro example you linked to -- adding f22 and f32 when your f16 has issues -- that's just bad engineering. Or a case of marketing running the show: "See, we have f32 too!"

I'm not quite as bitter as I sound right now, but when my $200 lens is beating the pants of off my $900 (plus the UV filter; $1000) lens, yeah -- I'm gonna be a little upset. Plus, I was really looking forward to the k20d, but if it's just so much hoopla there, too, well -- I may as well sell all of this stuff and join one of the two dark sides. It's been a year, I've just rolled the shot counter (10k shots on my k10d), and I've gotten to the point where I'm thinking... maybe it's NOT just me.

Oh, and -- how about the size difference? Those are identical crops from what are both supposed to be 50mm. Any thoughts?

Diffraction happens with ALL lenses, it's a fact of life!

Small apertures are required for increasing depth of field, not for increasing resolution. Nothing to do with the quality of engineering. Understand what it means, this may help:
Understanding Lens Diffraction

Regarding your 50mm question. Most lens focal lengths are calculated with their focus set at infinity, not at close distances, where they will differ somewhat. Try some distance shots, there could still be some small discrepancy, but it will be much less.

Back or front focus is another issue, all your lenses should be fairly close, if one is wildly out, then you should have the lens exchanged or serviced. If all your lenses are out by a similar amount, it points to faulty AF calibration of your camera, again it should be sent for calibration service.

02-10-2008, 04:57 AM	#43
Richard Day Pentaxian Location: Gloucester UK Gallery Photos: 0 Posts: 429	Originally Posted by amateur6 Thanks very much Richard! I'm going to do another round of test shots (actually I just did but I'm still getting a wicked back focus to correct). sigh Of course, the diffraction issue begs the question: can Pentax perhaps take a lesson from the elevator industry and please OVER-engineer instead of UNDER-engineering? In other words, if your f22 has issues, well, you shouldn't really have an f22, should you? Especially true of the 100mm Macro example you linked to -- adding f22 and f32 when your f16 has issues -- that's just bad engineering. Or a case of marketing running the show: "See, we have f32 too!" I'm not quite as bitter as I sound right now, but when my $200 lens is beating the pants of off my $900 (plus the UV filter; $1000) lens, yeah -- I'm gonna be a little upset. Plus, I was really looking forward to the k20d, but if it's just so much hoopla there, too, well -- I may as well sell all of this stuff and join one of the two dark sides. It's been a year, I've just rolled the shot counter (10k shots on my k10d), and I've gotten to the point where I'm thinking... maybe it's NOT just me. Oh, and -- how about the size difference? Those are identical crops from what are both supposed to be 50mm. Any thoughts? Diffraction happens with ALL lenses, it's a fact of life! Small apertures are required for increasing depth of field, not for increasing resolution. Nothing to do with the quality of engineering. Understand what it means, this may help: Understanding Lens Diffraction Regarding your 50mm question. Most lens focal lengths are calculated with their focus set at infinity, not at close distances, where they will differ somewhat. Try some distance shots, there could still be some small discrepancy, but it will be much less. Back or front focus is another issue, all your lenses should be fairly close, if one is wildly out, then you should have the lens exchanged or serviced. If all your lenses are out by a similar amount, it points to faulty AF calibration of your camera, again it should be sent for calibration service.