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04-26-2009, 02:39 PM   #16
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Diffraction limit is really lens dependent. Some limited lenses could push to aperture f16 without much image quality degradation.

04-26-2009, 06:10 PM   #17
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"Diffraction limit is really lens dependent. Some limited lenses could push to aperture f16 without much image quality degradation."

I don't think so, the 31mm f/1.8 limited performs VERY close to the diffraction limits from what I have observed, the FA 77 f/1.8 limited does equally as well. And the Pentax 50mm f/1.2 beats them both at f/2 and matches them at f/4-f/8 but beyond f/8 I fail to see any further increase of real resolution, yes sharpening increases that limit but sharpening only amplifies the detail that is there in the image. It can't recover detail that has been blurred to oblivion by diffraction.

BTW I tested the FA limiteds and the 50mm f/1.2 on Kodak technical pan film (developed in technidol) and verified the MTF 50% results from AGFAPAN 25 and Ilford Pan F both developed in Rodinol HR and the performance results are only applicable to the specific lenses I tested...your milage may vary. Those three lenses perform pretty much at the diffraction limit of 88 LPMM @ f/16 and to the best of my knowlege the K10D can resolve twice that amount of resolution.

all the figures and brain melting math, diffraction really isn't a HUGE issue. we also have to consider the noise that is inherent in all solid state imaging systems, and we can all stare at that until all we see is a blurry undefined mass... diffraction isn't likely to ruin your images, at least not for APS-C sensors with conservative pixel counts at the moment (well actually it is in regards to the 15Mp Canon 50D which I feel was a rather stupid marketing ploy, and nothing more). I feel really sorry for the four thirds camera users....
04-26-2009, 06:35 PM   #18
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QuoteOriginally posted by RioRico Quote
I ran the specs on some of my older Sony PNS's thru that site's Diffraction Limit Calculator and was gratified to find that my favorites, the 1.1mp DSC-P20 and 5mp DSC-V1 (both of which also have pretty low sensor pixel density), never reach a diffraction limit, which helps explain (besides the Zeiss optics on the V1) why their images are always crystalline - anything in focus is at maximum clarity. With their small sensors, the limits are fairly low - f/5.5 and f/4.7 respectively - but their tightest apertures are f/4.5 and f/4.0, well under those limits. Huzzah! And low pixel density means low noise (generally).
DPReview says that Sony DSC-V1 can be stopped down to f8
04-26-2009, 06:57 PM   #19
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QuoteOriginally posted by deejjjaaaa Quote
DPReview says that Sony DSC-V1 can be stopped down to f8
Dpreview also said that film is dead.

04-27-2009, 08:31 AM   #20
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Wow, thanks for all the info! Yes, the V1 *can* be stopped down to f/8 in A or M mode - I just verified that. Duh, I shoulda gotten outa P mode, where f/4 *is* the end. Again, I see diffraction limits as an issue primarily at extreme magnification of detailed images, especially wides, teles, and macros. Most of my shots *don't* go to extremes. I don't usually worry about knife-edge sharpness; (all too) many of my images are artistically soft - I like to cite a UC Berkeley photo prof that the art is not in the resolution, it's in the forms. And yes, I'll have to do some empirical testing and pixel-peeping on my own, to establish my own limits of acceptability. I just like getting theoritical input first. (What, field-testing?!? Leave the keyboard?!? Shudder...)
05-07-2009, 09:47 AM   #21
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QuoteOriginally posted by RioRico Quote
I know that other members here, like falconeye and Ben Edict, have written knowledgibly on diffraction. I'm sorta appealing to them for clarification. Help!
Do I see my name here ?

Well, for easier reference by others researching the issue, I'll refer to my post first, where I tried to sum it all up.

It studied 2 different comparisons:

STUDY:

We compare two cameras, with same pixel count but different sensor size, and the camera with the smaller sensor has a focal length smaller by the same factor, too. Where:
(A) Both cameras use a lens of exactly the same physical diameter in mm.
(B) Both cameras use a lens of exactly the same f-stop number.

Read it all here:
https://www.pentaxforums.com/forums/459034-post21.html



With respect to your original question, I noticed that you already confused circle of confusion with pixel size.

---

To sum up my answer above with respect to diffraction:

Take situation (A). Here you see that the diffraction effect (as far as a printed photo would be concerned) is independent from the sensor size. But because smaller sensor cameras tend to go with smaller diameter lenses they tend to hit the diffraction limit sooner (in real photography practical terms).

As for the resolution limit:

The limit is where two Airy disks overlap at distance of radius r (formula above r = 1.22 lambda N), i.e., where a line pair has width r and a line (pixel) has width r/2. But at that limit, you are left with marginal contrast only and you would need a lot of sharpening.

For practical purposes, you double this and require r <= feature size.

Where feature size is pixel size (pixel peeping) or circle of confusion CoC, whatever is your requirement.

K20D: Pixel = 5 µm, CoC = 20 µm.


So, the most obscene requirement translates to:

N <= 5 µm / (1.22 lambda) ~= 8

but the naked eye won't see diffraction on a print on the wall if

N <= ~ 32 (i.e., never).



Nevertheless, the best one or two 35mm SLR lenses are so good that diffraction makes them resolve best at f/2.8! And only quite bad lenses resolve better at f/8 than at f/5.6.


If you have to trade softness from DoF against diffraction, the 100 y.o. term "Förderliche Blende" comes to mind ... (critical / usable aperture)

Last edited by falconeye; 05-07-2009 at 10:01 AM.
05-10-2009, 02:02 AM   #22
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QuoteOriginally posted by roentarre Quote
Diffraction limit is really lens dependent. Some limited lenses could push to aperture f16 without much image quality degradation.
Is this why Canon sells some lenses labled DO (Diffractive Optics?)
05-10-2009, 06:12 AM   #23
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no DO lenses are bound by the same laws that all optical instruments are. nor are they diffraction limited lenses.

05-10-2009, 09:45 AM   #24
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QuoteOriginally posted by res3567 Quote
Is this why Canon sells some lenses labled DO (Diffractive Optics?)
DO is a Canon-specific technology that allows them to make average-performing but very expensive compact telephoto lenses. It uses glass shaped similarly to Fresnel lenses.
05-10-2009, 11:04 AM   #25
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QuoteOriginally posted by Digitalis Quote
no DO lenses are bound by the same laws that all optical instruments are. nor are they diffraction limited lenses.
QuoteOriginally posted by ftpaddict Quote
DO is a Canon-specific technology that allows them to make average-performing but very expensive compact telephoto lenses. It uses glass shaped similarly to Fresnel lenses.
I wondered why they cost so much but did not have the same specs as thier L lenses.

What is the advantage of a DO lens anyway?
05-10-2009, 12:41 PM   #26
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So images get mildly softer when you stop down to a certain point. It probably isn't that noticable.
05-10-2009, 04:55 PM   #27
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"What is the advantage of a DO lens anyway?"

without getting too technical, DO lenses are often smaller and lighter than than normal lens designs. however the image they produce need a good deal of sharpening to get them to look "normal" again. and these lenses have one trait in common with mirror lenses...rings in the bokeh, out of focus highlights from DO lenses look more like ripples in a pond. it's a strange effect and it can create some truly ghastly bokeh.
05-10-2009, 04:59 PM   #28
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QuoteOriginally posted by Cosmo Quote
So images get mildly softer when you stop down to a certain point. It probably isn't that noticable.

no, it's when you stop down PAST a certain point which is related to the pixel size of your DSLR.

that's it in a nutshell. it isn't a huge problem and all DSLRs suffer from it, don't lose any sleep about it.

Last edited by Digitalis; 05-10-2009 at 06:21 PM.
05-12-2009, 09:34 AM   #29
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QuoteOriginally posted by Digitalis Quote
no, it's when you stop down PAST a certain point which is related to the pixel size of your DSLR.
So what happens when you stop down past that certain point?
05-12-2009, 10:22 AM   #30
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All interested parties can look at pp. 17-23 of "Photo Techniques", Jan/Feb 2009. The article is "Diffraction: Resolution taxed to its limits" by Lloyd L. Chambers.

The author shot resolution charts with Canon EOS 1Ds Mark III & Nikon 85mm f/2.8 D PC-Micro-Nikkor,
as well as Nikon D3 & Nikon 85mm f/2.8 D PC-Micro-Nikkor.

This is his comment about his "real world" shots of San Francisco: "By f/16, however, the trend is clear: contrast drops and the image begins to look flat, though actual resolved detail is still present. Apertures f/22, f/32 and f/45 worsen progressively."

Note that K20D's pixel density is greater than both the Canon and the Nikon tested.
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