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12-03-2012, 06:56 PM   #1
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Diffraction and our Q

It’s been cold and raining here in Michigan for several days and it’s getting to me so I started searching for information about Diffraction and our Q. After searching this forum and doing a lot of reading on the Cambridge in Color Web pages on diffraction I find myself still somewhat confused.

Per the Cambridge in Color site for our beloved Q the range of diffraction onset is from f2.4 to f3.6. This is assuming a "perfect lens" per the site. I know my lenses are far from perfect so what does this mean to me. I did a test photographing a resolution chart with all the lenses I adapted on my Q. Shooting from wide open to f8 assuming f8 to be in full diffraction on my Q. All lenses tested on my Q on a tripod and using a 10sec. timer to trip the shutter. Here is what I found to be the sharpest aperture for my lenses

SMC-A 28 f2.8 is sharpest at f5.6
DA 35mm f2.4 is sharpest at f4
SMC-A 50mm f1.7 is sharpest at f4
SMC-M 135 f3.5 is sharpest at f5.6
SMC Pentax 200 f4 is sharpest at f5.6
Tamron 70-300 f4-5.8 shot at 300 is sharpest at f5.6
DAL 55-300 is sharpest at f5.6

I guess this means my lenses are far from perfect and the 35 & 50 are my sharpest lenses as they are is diffraction limited at the lowest aperture. They are also rated highest for IQ for all my lenses in PF lens reviews

Hans


Last edited by hnikesch; 12-26-2012 at 02:08 PM.
12-03-2012, 07:01 PM   #2
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I think, that most lenses generally reach sharpest around F5.6 to F8, with the odd outliers at F4 or F11. I think what you are looking for are lenses that are acceptably sharp within the F2.4 to F3.6 range - not maximum sharpness...
12-03-2012, 07:26 PM   #3
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QuoteOriginally posted by JinDesu Quote
I think, that most lenses generally reach sharpest around F5.6 to F8, with the odd outliers at F4 or F11. I think what you are looking for are lenses that are acceptably sharp within the F2.4 to F3.6 range - not maximum sharpness...
What I was testing for was how best to shoot the lenses I have on my Q while looking for something better. My lenses shoot a sharper image when stopped beyond diffraction on my Q

Hans

Last edited by hnikesch; 12-03-2012 at 07:50 PM.
12-03-2012, 07:30 PM   #4
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Yes, but I don't think there are many (if any) lenses that are sharpest at F2.4-3.6 AND sharper than say the FA 50 1.7.

12-03-2012, 08:03 PM   #5
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I see the Q has shutter speeds up to 1/2000 and 1/8000 and max aperture f/8
What print / monitor dimensions are typical with reasonably sharp images for viewing Q photos?
12-03-2012, 08:04 PM   #6
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QuoteOriginally posted by JinDesu Quote
Yes, but I don't think there are many (if any) lenses that are sharpest at F2.4-3.6 AND sharper than say the FA 50 1.7.
The Q standard prime maybe? Quite possibly also the telezoom. I would expect some of the sharper K lenses to also qualify in the area relevant on the Q. FA31 maybe? (Ridiculous to use it on a Q of course.)
12-03-2012, 08:11 PM   #7
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QuoteOriginally posted by drougge Quote
The Q standard prime maybe? Quite possibly also the telezoom. I would expect some of the sharper K lenses to also qualify in the area relevant on the Q. FA31 maybe? (Ridiculous to use it on a Q of course.)
I believe the FA 31's sharpest at F4. Of course, it's plenty sharp at F2.4-F3.6, but... then again, several of his lenses are already very good candidates in that range (A28 F2.8, DA 35 F2.4, A50 1.7)
12-03-2012, 10:02 PM   #8
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QuoteOriginally posted by JinDesu Quote
I believe the FA 31's sharpest at F4. Of course, it's plenty sharp at F2.4-F3.6, but... then again, several of his lenses are already very good candidates in that range (A28 F2.8, DA 35 F2.4, A50 1.7)
I guess I didn't make myself very clear, I didn't test to find the sharpest lens or at what aperture my lenses are the sharpest, I tested to find the best aperture to shoot my lenses when adapted to my Q. The articles on diffraction state that our Q will start seeing diffraction on a perfect lens at f2.8 but a not so perfect lens may actually provide a sharper image stopped down beyond diffraction. I realize that image will not be as good as a perfect lens not diffracted. But it will be as good as that lens can get on my Q. Combining a sharper aperture and some diffraction on my lenses is better rather than a soft aperture and no diffraction. Does any of this make any sense or am I way off the deep end.

My reason for getting a Q is to do things I can't do with my lenses on my Kr or with my P&S. I wanted something longer than 300mm (450 w/crop factor) for a reasonable price and the closeup options the Q provides with adapted lenses.

Hans


Last edited by hnikesch; 12-03-2012 at 10:08 PM.
12-03-2012, 10:03 PM   #9
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That's makes a lot more sense, because I thought you were trying to find a lens that was sharpest only at F2.4-3.6, which is very limiting.
12-03-2012, 10:23 PM   #10
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QuoteOriginally posted by hnikesch Quote
Here is what I found to be the sharpest aperture for my lenses
How could you tell for sure what aperture your DA and DAL lenses were at? I've been trying to figure this out, thanks.
12-03-2012, 11:58 PM   #11
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QuoteOriginally posted by hnikesch Quote
It’s been cold and raining here in Michigan for several days and it’s getting to me so I started searching for information about Diffraction and our Q. After searching this forum and doing a lot of reading on the Cambridge in Color Web pages on diffraction I find myself still somewhat confused.

Per the site for our beloved Q the range of diffraction onset is from f2.4 to f3.6. This is assuming a "perfect lens" per the site. I know my lenses are far from perfect so what does this mean to me. I did a test photographing a resolution chart with all the lenses I adapted on my Q. Shooting from wide open to f8 assuming f8 to be in full diffraction on my Q. All lenses tested on my Q on a tripod and using a 10sec. timer to trip the shutter. Here is what I found to be the sharpest aperture for my lenses

SMC-A 28 f2.8 is sharpest at f5.6
DA 35mm f2.4 is sharpest at f4
SMC-A 50mm f1.7 is sharpest at f4
SMC-M 135 f3.5 is sharpest at f5.6
SMC Pentax 200 f4 is sharpest at f5.6
Tamron 70-300 f4-5.8 shot at 300 is sharpest at f5.6
DAL 55-300 is sharpest at f5.6

I guess this means my lenses are far from perfect and the 35 & 50 are my sharpest lenses as they are is diffraction limited at the lowest aperture. They are also rated highest for IQ for all my lenses in PF lens reviews
Hi Hans,

IMO, this is about the most practical post I've seen about diffraction and the Q. I'd suggest that anyone wanting to use adapted lenses for super tele with the Q do a similar test with the lenses that they plan to use with the Q. Example variation/mfg tolerances plus the fact that each lens design has a different "sweet spot" suggests that some may gain more resolution from stopping down than they lose to diffraction, so a general "don't shoot past f (x) aperture" shouldn't be taken as a general rule, IMO. Also, IQ is totally subjective, as are PP skills. A shot that one person considers a bin candidate might be fine for another's use, especially if they are particularly skilled at PP, and/or have superior processing tools. Intended display media and format is also a variable for what might be "acceptable" for IQ. Each shooter needs to decide for him/her self, and an experiment like you used seems a very good way to discover where each lens stands.

Scott
12-04-2012, 04:06 AM   #12
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QuoteOriginally posted by JinDesu Quote
I believe the FA 31's sharpest at F4. Of course, it's plenty sharp at F2.4-F3.6, but... then again, several of his lenses are already very good candidates in that range (A28 F2.8, DA 35 F2.4, A50 1.7)
Photozone disagrees. Not that the difference shown looks relevant, but that's on a K5. On the Q the difference might well be bigger.

Generally speaking the "best" f-stop should be lower on a Q, since people don't just care about the very center, but that's where lenses get sharp first. (The Sigma DC 30mm would probably do well on the Q, at least resolution-wise.)

But this is in theory, and hnikesch tried it in practice, where this doesn't really seem to be true (I expect the same f-stop to win on a K5).
12-04-2012, 06:27 AM   #13
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QuoteOriginally posted by crewl1 Quote
How could you tell for sure what aperture your DA and DAL lenses were at? I've been trying to figure this out, thanks.
I wasn't very scientific I just counted clicks on my on my Fotodiox so it's an assumption but as long as I remember the number of clicks (AD 35 2.4 was 2 clicks and the 55-300 was 1) I should be OK. On my Tamron for my test the aperture ring was set at f5.6 but because the aperture decreases as you zoom out to the actual best aperture @ 300mm was closer to f7

Hans

Last edited by hnikesch; 12-04-2012 at 06:52 AM.
12-04-2012, 06:41 AM   #14
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QuoteOriginally posted by drougge Quote
Photozone disagrees. Not that the difference shown looks relevant, but that's on a K5. On the Q the difference might well be bigger.

Generally speaking the "best" f-stop should be lower on a Q, since people don't just care about the very center, but that's where lenses get sharp first. (The Sigma DC 30mm would probably do well on the Q, at least resolution-wise.)

But this is in theory, and hnikesch tried it in practice, where this doesn't really seem to be true (I expect the same f-stop to win on a K5).
The K5 should allow for lower apertures than the Q because per the Diffraction Limited Aperture Calculator on the Cambridge in color site the range of diffraction onset on the K5 is f6.3 to f10.3 the Q is f2.4 to f3.6. If a lens has a sweet spot at an aperture lower than f6.3 the K5 will provide a sharper image than the Q. Per the photozone tests on my Tamron 70-300 and DAL 55-300 I shot both at f8 on my Kr but because of my test i will shoot both at f5.6 on the Q

Hans
12-04-2012, 06:57 AM   #15
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Hi Scott I see you understand and that you couldn't sleep 2AM??, I had been shooting my long lenses wide open and not very happy with the results, for me this was an eye opener

Hans
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