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Author Topic: Understanding Lens Diffraction  (Read 5358 times)

Jim Kasson

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Re: Understanding Lens Diffraction
« Reply #60 on: June 14, 2019, 10:05:55 am »



It would have been interesting to learn, had Adams had the possibility of focus-stacking like we do today, what he would have done ...



He did have the ability to do tilts, and he used that to the fullest. He was also a techie. So he probably he would have used stacking if that would produce an image that better fulfilled his objectives.



Jim

HSakols

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Re: Understanding Lens Diffraction
« Reply #61 on: June 15, 2019, 07:42:24 pm »

Thank all for the feedback and examples.  Thanks especially to Erik for spending the time to respond with much wisdom.  So for those of us that will continue capturing at f11 - f22, what is the best way to apply deconvolution sharpening?  Is this accomplished with Adobe Lightroom?  What about Focus Magic? And no I"m not suggesting that it cures the effects of diffraction.  I'm interested in fine art printing. 
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Martin Kristiansen

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Re: Understanding Lens Diffraction
« Reply #62 on: June 16, 2019, 01:31:43 am »

Thank all for the feedback and examples.  Thanks especially to Erik for spending the time to respond with much wisdom.  So for those of us that will continue capturing at f11 - f22, what is the best way to apply deconvolution sharpening?  Is this accomplished with Adobe Lightroom?  What about Focus Magic? And no I"m not suggesting that it cures the effects of diffraction.  I'm interested in fine art printing.

I am using Capture 1 which has a setting to remove diffraction.I am not sure how good it is and would be interested in what the real experts have to say on this matter. It’s my understanding that the softness caused by diffraction would be uniform across the image.  Ames it easy to apply a global setting per lens per aperture.

To be clear I don’t advocate ignoring diffraction. When depth of field is not important it is sloppy to use a small aperture. Better to adjust iso or shutter speed to hit the sweet spot on your lens.
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Bart_van_der_Wolf

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Re: Understanding Lens Diffraction
« Reply #63 on: June 16, 2019, 06:14:58 am »

Thank all for the feedback and examples.  Thanks especially to Erik for spending the time to respond with much wisdom.  So for those of us that will continue capturing at f11 - f22, what is the best way to apply deconvolution sharpening?  Is this accomplished with Adobe Lightroom?  What about Focus Magic? And no I"m not suggesting that it cures the effects of diffraction.  I'm interested in fine art printing.

FocusMagic remains to be a very useful and robust tool.
The implementation in ACR is of lower quality, but some use a very low amount and a high 'Detail' setting.

Like Martin, I use Capture One Pro as Raw converter, and it has a built-in option to correct for diffraction, and it is quite effective.

Cheers,
Bart
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ErikKaffehr

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Re: Understanding Lens Diffraction
« Reply #64 on: June 16, 2019, 02:55:14 pm »

Hi,

I would second the comment on FocusMagic.

In retrospective, I would say that many of my prints are oversharpened. I like Lightroom, and it is my main tool, but I think that other programs may have better demosaic.

Having a setting for compensating diffraction is basically a good thing, at least if correctly implemented.

Best regards
Erik


FocusMagic remains to be a very useful and robust tool.
The implementation in ACR is of lower quality, but some use a very low amount and a high 'Detail' setting.

Like Martin, I use Capture One Pro as Raw converter, and it has a built-in option to correct for diffraction, and it is quite effective.

Cheers,
Bart
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Erik Kaffehr
 

BJL

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With “normal sized” prints from 35mm film cameras, I think it was fairly well-known that at about f/22 or a bit beyond, images start to get a bit soft, moving towards the pin-hole camera effect as you stop down further: that’s diffraction. For those of us who still display and view images in “normal” fashion, from not closer than the long dimension of the image, diffraction continues to be a visible factor only at or beyond the smallest apertures that cameras offer. But likewise, such display/viewing style does not benefit in visible sharpness from going beyond about 12MP—maybe 24MP as a generous estimate.

This discussion of diffraction is therefore mostly relevant to those who are using the newer higher resolution cameras and want to make good use of the extra sensor resolution: “big prints viewed up close” so that only a part of the scene is being seen at a time, rather than “holistic” viewing.

For this case, I suggest a simple procedure. First find at what apertures you see significant “pinhole softening” in normal viewing, for which about 6-12MP gives all the needed sharpness. Then for each doubling of pixel count—and thus doubling of print area if you aim at the same viewing distance and print PPI—reduce that “pinhole softening threshold” one stop. If however that gives too little DOF so that improving sharpness of the in-focus subjects causes unacceptable loss of sharpness elsewhere in the image, stay with the smaller aperture—and accept that the latest upgrade of your pixel count is of no value for this particular composition. If that happens most or all of the time, congratulations: the MP race is over for you! (As it is for me and my style of photography.)

One catch though: each doubling of pixel count and intended print size (with equal viewing distance) makes that OOF blurring more visible, so not only might you want not to open up one stop to keep the main subject fully sharp; you might actually want to stop down to protect other parts of the scene from too much OOF softening. Which means that the maximum worthwhile pixel count—and maximum print size at which everything you want sharp does like look sharp—is even more limited by the closing twin jaws of diffraction and OOF effects.

Maybe focus stacking is a partial way out; e. g. several diffraction-free images at f/5.6 or f/8 rather than the f/11 or f/16 that your DOF needs dictates.
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Slobodan Blagojevic

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Re: Understanding Lens Diffraction
« Reply #66 on: June 17, 2019, 09:50:48 am »

Ah, the battle of masterbators vs. measurbators!  Or photographers vs. engineers ;)

BJL

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Re: Understanding Lens Diffraction
« Reply #67 on: June 17, 2019, 11:41:42 am »

Ah, the battle of masterbators vs. measurbators!  Or photographers vs. engineers ;)
C’mon Slobodan: anyone who bothers to use a camera with way more resolution than “normal” printing and viewing requires (more than about 12 MP?) needs to understand all the factors that might affect image sharpness; otherwise they risk being seen as money-wasting dilettantes. In the high resolution realm, thinking about how aperture affects diffraction (or as I call it, “the pinhole camera effect”) and thus sharpness is no more esoteric, irrelevant or “geeky” than thinking about how aperture choice affects DOF or how shutter speed affects motion blur.

Diffraction was only less discussed in the film era because apertures small enough to produce diffraction effects were usually way smaller than typically chosen for adequate DOF, and even beyond the f-stop scale of most 35mm format lenses.
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Slobodan Blagojevic

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Re: Understanding Lens Diffraction
« Reply #68 on: June 17, 2019, 12:12:11 pm »

C’mon Slobodan...

Note the smiley in my comment.

Ever since I learned photography (in the film era, many years ago), I've been aware of diffraction. As a practicing photographer that is more concerned with the moment and light than fiddling with diffraction and dof calculators, Ive been using a simple rule of thumb: avoid the first and last two f/stops, if you can.

There are photographers, however, that seem to have heard only the "first two f/stops " part. They extrapolate that to mean "you get sharper photos with less optical aberrations as you keep closing the f/stop, so the further you go, the better it gets." I've been seeing super wide-angle shots using f/22, where nothing in the foreground to suggest it is needed. Those are the folks that would benefit from this discussion.
« Last Edit: June 17, 2019, 01:39:05 pm by Slobodan Blagojevic »
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BJL

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Re: Understanding Lens Diffraction
« Reply #69 on: June 17, 2019, 12:43:30 pm »

Slobodan, yes I was almost one of those people when young: always stopping down as much as adequate shutter speed allowed. And now using 4/3” format with its very high lp/mm sensor resolution, it is worth knowing that diffraction starts to hurt at distinctly lower f-stops; in general, at half the f-stop where I would start worrying in 35mm format when aiming for an equally large print. So for example, f/16 is usually unwise, except when some macro situations struggle for DOF; that worry would only have arisen at f/32 or beyond in my film camera days, when I was also enlarging less due to the lower resolution of the color film I was using.
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Rob C

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Re: Understanding Lens Diffraction
« Reply #70 on: June 17, 2019, 04:39:43 pm »

Ah, the battle of masterbators vs. measurbators!  Or photographers vs. engineers ;)

It's fun
For some.

Thank God I never wanted to do landscapes! My people all looked crisp enough or blurry enough as I wanted them to look. The important bit was 64 ASA and making the most of it.

If you have an f8/500 cat lens, you don't have to lose sleep: shoot as it comes! (How much better the results had I been shooting it digital with ISO at whatever was required! I came too soon or, rather, my time did.)

Had anyone come up close, sniffing 'em (the pix), I'd have thought them (the sniffers) freakin' perverts.

:-)
« Last Edit: June 17, 2019, 04:45:12 pm by Rob C »
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