Diffraction Myth Dispelled

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brainiac
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p.1 #1 · Diffraction Myth Dispelled

I have read a fair number of comments on this forum and some others about how diffraction will totally, like, DOOM your images if you use a camera with a densely populated sensor, or apertures above f8 and so on. It's all a storm in a teacup. Here are some unscaled crops from a 1Ds3 using 3 different 35mm lenses at f5.6, and f16. The diffraction effects were so minor that I decided to see how many sharpening clicks they amounted to in DPP. The answer is 2 or 3. The blurring is on such a small scale that sharpening seems to overcome it completely. One of the lenses was an f1.4, so I regard its performance at f16 as a total refutation of the nonsense that gets talked about diffraction. In fact, overall the f16 performances were perhaps preferable, since corner performance was superior on all three lenses at this aperture. I am looking forward to the 30 megapixel 135 format DSLR.

Who can see which images are at f5.6, and which are f16?

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Oct 07, 2008 at 04:29 PM

Evan Baines
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p.1 #2 · Diffraction Myth Dispelled

Braniac,

Interesting results. I'm surprised that you've seen people talking about diffraction at f/16 as a huge issue. Most lenses (except some of the ultra fast primes) peak in the f/8 to f/11 range, but most good lenses won't show significant results from diffraction until you go past f/16. F/22 is where it usually really starts to show up in prints, to the point where on some lenses the overall MTF actually drops below wide-open.

Oct 07, 2008 at 04:34 PM

brainiac
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p.1 #3 · Diffraction Myth Dispelled

BTW, the lenses are a Nikon, a Canon, and a Zeiss. No clues.

Oct 07, 2008 at 04:36 PM

brainiac
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p.1 #4 · Diffraction Myth Dispelled

Evan Baines wrote:
I'm surprised that you've seen people talking about diffraction at f/16 as a huge issue.

It's a particular favourite on some forums, for obvious reasons. It's also popular with people who like to compare 100% crops at differing magnification and declare the lower megapixel camera the winner. The third group who enjoying spreading this fud are those who have never used a 15, 16.7, 21 or 24 megapixel camera and can't, for the moment, justify buying one. ;-)

Oct 07, 2008 at 04:40 PM

Beni
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p.1 #5 · Diffraction Myth Dispelled

I see 'lack of sharpness' whether lens or diffraction based kicking in by f8 on my 5D in real life work. The difference in sharpness and resolution between f16 and f22, after sharpening, is huge. This is with the 50mm 1.4, 50mm Macro and 70-200 f4L IS. I've never shot that stopped down (past 5.6) with any of my other lenses so I can't comment.

Given the huge divide between f16 and f22 on my 5D (Knocks it down to less than 10 megapixels worth) I would assume that the same would only be more so with a higher resolving sensor, either due to the higher diffraction or just because differences in resolving detail would be magnified. Either explanation for the sharpness difference and it's certainly not to be ignored. I have to admit that I've been too scared to compare f16 and f11, I've no doubt there is yet again a noticeable difference.

Listen, I know Braniac has a bee in his bonnet about diffraction but all the tests and experiece of people I trust shows that the 1Ds mkIII is diffraction limited from about f11 and maybe even f5.6. Diffraction isn't a made up word by scientists, it's a real world phenomenon. I see it on my 5D and have no doubt whatsoever that at the f-stops I would need for my high resolution needs it was enough for me to be pursuaded that there would be little to no advantage in buying a 1Ds mkII for f16-22 use rather than my present 5D's. As such I'm stitching to get a real resolution bump when stopped down and even stitching DOF.

This first image below is softer for being shot at f22, but when the stitched image is the equivelent of 30 megapixels I don't mind so much! Even so the slight softness is there (at 100% but then I'm printing it at 36X18") however much I sharpen it. The 2nd stitched image was shot at f16 and is a whole heck of a lot sharper.

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Oct 07, 2008 at 04:56 PM

edwardkaraa
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p.1 #6 · Diffraction Myth Dispelled

Diffraction depends on the sensor/film format and aperture. Small P&S sensors experience diffraction at f/8, while FF should be good until f/16. It's no different than during film days, it's just not many people could afford to blow up images at 100x150 cm and inspect them at 20 cm distance for diffraction. The moral of the story, more MP do not produce more diffraction, they just allow you to enlarge more and you enlarge everything at the same time, hand-shake blur, small focusing errors, lens imperfections and diffraction. This is another internet myth.

Oct 07, 2008 at 05:10 PM

Sam N
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p.1 #7 · Diffraction Myth Dispelled

brainiac wrote:
It's all a storm in a teacup.

Tempest... a tempest in a teacup.

Absolute sharpness isn't the most important thing, and diffraction is real but ultimately not that big of a deal in most cases. I have noticed that my shots at F22 and above don't look as good as those at F8 or F11, but not by a huge amount.

Oct 07, 2008 at 05:44 PM

brainiac
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p.1 #8 · Diffraction Myth Dispelled

To clarify, I'm not saying diffraction doesn't exist. I am saying that it isn't DOOM for a photo, and a 1Ds3 can deliver good results at f16, with appropriate sharpening.

Oct 07, 2008 at 05:47 PM

Weiyang Liu
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p.1 #9 · Diffraction Myth Dispelled

brainiac, I'm unfamiliar with people that say that photos get doomed at f16 for a full frame sensor @ 20+ MP. The few instances where I've seen people claim make that claim have been followed by other people who immediately shoot down that claim. What's common though is the claim that you start seeing major diffraction problems when you push past f/16, say at f/22 or above.

I wouldn't be surprised if you took a shot at f/22 for the above scene that you will start seeing softness at those unscaled crops....of course, still not visible if you print to 8x12.

Oct 07, 2008 at 05:56 PM

mh2000
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p.1 #10 · Diffraction Myth Dispelled

Oh come on! This whole forum is dedicated to people who think anything less than the very sharpest lenses, corner to corner, spells absolute doom!

brainiac wrote:
To clarify, I'm not saying diffraction doesn't exist. I am saying that it isn't DOOM for a photo, and a 1Ds3 can deliver good results at f16, with appropriate sharpening.

Oct 07, 2008 at 06:12 PM

UCSB
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p.1 #11 · Diffraction Myth Dispelled

Brainiac ... this demo would be more useful if you labeled the images (lens, aperture, sharpening settings) so a comparison can be made. Why did you upscale your crops? Thanks for making the point that diffraction won't kill our 5DII images at f/16.

Oct 07, 2008 at 06:21 PM

Andi Dietrich
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p.1 #12 · Diffraction Myth Dispelled

Diffraction may be a problem when shooting close up. There is a point where the lens will go noticably less sharp and you will need to find the best compromise between diffraction and DOF. However this is no problem unless you need to have the full resolution of the system.

I suspect that the AA filter hides some of the visible diffraction, at least I think systems without it "suffer" more from diffraction. True?

Oct 07, 2008 at 06:31 PM

Jman13
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p.1 #13 · Diffraction Myth Dispelled

Looking at these, assuming they're paired 1,2 - 3,4 - 5,6.

#2 looks a tiny bit better than #1.
#3 looks a tiny bit better than #4
I see no perceptible difference in 5 & 6.

I agree with you, though. If you need the DOF, the sharpness lost to diffraction is nothing compared to losing the DOF you need. I use small apertures when I need to, and larger ones when I don't.

Oct 07, 2008 at 06:31 PM

brainiac
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p.1 #14 · Diffraction Myth Dispelled

Jman13 wrote:
Looking at these, assuming they're paired 1,2 - 3,4 - 5,6.

#2 looks a tiny bit better than #1.
#3 looks a tiny bit better than #4
I see no perceptible difference in 5 & 6.

I agree with you, though. If you need the DOF, the sharpness lost to diffraction is nothing compared to losing the DOF you need. I use small apertures when I need to, and larger ones when I don't.

Thanks for having a punt. I'll say what they are when someone else has had the balls to have a guess. ;-)

Oct 07, 2008 at 06:41 PM

Seth Tower
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p.1 #15 · Diffraction Myth Dispelled

Every lens is different. I get very good results from my 24-105L stopped down well past f/16 with it's 8 blade circular aperture. Ditto the 70-200 2.8L IS. My 35 2.0, with an ancient 5 blade non-circular aperture, is a different story. At f/16, diffraction is noticeable throughout the photo (especially at 100%); at f/22, there is so much diffraction it literally looks like the image was pulled diagonal through a taffy-pull; it's completely unusable except in the smallest prints.

Thus, the more blades and the rounder the aperture is (when stopped down), the less diffraction there will be.

Oct 07, 2008 at 06:47 PM

Seth Tower
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p.1 #16 · Diffraction Myth Dispelled

2, 3, & 5 are f/16

Oct 07, 2008 at 06:52 PM

Ariel Bravy
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p.1 #17 · Diffraction Myth Dispelled

Looks like, assuming each lens is paired 1,2 - 3,4 - 5,6 as Jman13 said (I wish you would have told us at least this much), the second image tends to be better than the first, but the difference is smallest with the last set.

I'm curious to see how much of a difference there'd be if you actually went down to f22 or f32.

Is there a difference in sharpness between peak and stopped down? Sure. Is it very noticeable? Depends. Some of the macro guys won't stop down beyond f5.6 on an f2.8 lens (MP-E 65), for example, because sharpness takes such a drastic hit and so they'll focus stack multiple images instead. Granted, the MP-E is somewhat of an exception because its effective aperture is something wayyyyy smaller than f5.6, but still.

Has anyone compared the softness of a lens wide open with the softness stopped all the way down? I'm curious...

Oct 07, 2008 at 06:55 PM

Seth Tower
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p.1 #18 · Diffraction Myth Dispelled

Ariel Bravy wrote:
Has anyone compared the softness of a lens wide open with the softness stopped all the way down? I'm curious...

Yes. Most of the lenses I've tested are sharper wide open rather than at minimum aperture. These include: 24-105L, 70-200 2.8L IS, 10-22, 18-55, 24 2.8, 35 2.0 & 50 1.8. The 50 1.4 is an exception as it's quite soft wide open; thus it's sharper at f/22. Of course, if you stop it down to 1.6 or 1.8, it sharpens up significantly.

Oct 07, 2008 at 07:01 PM

brainiac
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p.1 #19 · Diffraction Myth Dispelled

OK, 1, 3, and 5 are f16. The first two are the Nikkor 35 f2, the second pair are the Canon 35 f2, and the last two are the Zeiss 35 f1.4(!).

Overall I felt the competition between these lenses was a draw. The Canon 35 f2 was consistently the sharpest over the majority of the frame, but at most apertures the corners were so disgusting that it really affected the general feel of the picture. It also had runaway contrast in the highlights and foggy clouds around any very bright points. The Zeiss was superb in the centre, but zone B wasn't any better than the Nikon, and often worse than the Canon. From f4 upwards the Zeiss had the best corners, but the Nikon put in the most even performance, if unexceptional. All things considered, I'll keep using the Zeiss. It had a lovely ability to retain highlights while keeping the shadows punchy. My 35L was sharper in the corners than the Zeiss, but I still sold it because there is something special about the Zeiss's rendition. Sharpness isn't everything, I suppose.

By the way, the telltale was the occluded 'Gypsy Princess' text. In 1, 3, and 5 you can see that it has had more sharpening, and has jaggier edges.

Edited on Oct 07, 2008 at 07:11 PM · View previous versions

Oct 07, 2008 at 07:06 PM

Seth Tower
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p.1 #20 · Diffraction Myth Dispelled

brainiac wrote:
OK, 1, 3, and 5 are f16.

It must have been windy then, because the leaves are clearly sharper in shot 2 vs 1.

Oct 07, 2008 at 07:08 PM

brainiac
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p.1 #21 · Diffraction Myth Dispelled

Seth Tower wrote:
brainiac wrote:
OK, 1, 3, and 5 are f16.

It must have been windy then, because the leaves are clearly sharper in shot 2 vs 1.

;-) lens test rule 1: never trust leaves

Oct 07, 2008 at 07:12 PM

Anon Moss
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p.1 #22 · Diffraction Myth Dispelled

OT to the OP...
I just hope that you don't swim in that water - Yuck!

Oct 07, 2008 at 07:17 PM

danmitchell
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p.1 #23 · Diffraction Myth Dispelled

brainiac wrote:
I have read a fair number of comments on this forum and some others about how diffraction will totally, like, DOOM your images if you use a camera with a densely populated sensor, or apertures above f8 and so on. It's all a storm in a teacup...

I'm pretty much in agreement with you here, based on both understanding of how this works and on my photographic results.

My favorite bogus claim is that "you'll get more diffraction if you increase photosite density" or similar words. Sheesh. Just plain wrong. You get the same diffraction blur at a given aperture with a given lens in a given format whether your sensor has 24MP or 2 MP. (You may get a more accurate rendition of the diffraction in one case, but no more or less.)

I also find the way that the term "diffraction limit" is used and apparently understood by many posters to be disconnected from actual photography. You'll read things like "camera X is diffraction-limited at f/5.6." The follow on assumption seems to be that you are "limited" to apertures no smaller than f/5.6 due to diffraction. Again, nonsense. There is much that could be said about this, but I'll just point out that in certain scenes DOF is more critical to producing the desired result than is absolute maximum sharpness.

I'll stop now. :-)

Dan

Oct 07, 2008 at 07:18 PM

danmitchell
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p.1 #24 · Diffraction Myth Dispelled

Seth Tower wrote:
Every lens is different. I get very good results from my 24-105L stopped down well past f/16 with it's 8 blade circular aperture. Ditto the 70-200 2.8L IS. My 35 2.0, with an ancient 5 blade non-circular aperture, is a different story. At f/16, diffraction is noticeable throughout the photo (especially at 100%); at f/22, there is so much diffraction it literally looks like the image was pulled diagonal through a taffy-pull; it's completely unusable except in the smallest prints.

Thus, the more blades and the rounder the aperture is (when stopped down), the less diffraction there will be.

I read some follow-up on this conjecture elsewhere. It turns out that any effect that the aperture shape would have on the amount of diffraction is vanishingly small. If you are having sharpness issues with lenses that have different numbers of blades, any significant differences are virtually certain to be caused by something other than diffraction.

Dan

Oct 07, 2008 at 07:20 PM

ChrisDM
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p.1 #25 · Diffraction Myth Dispelled

I wouldn't call diffraction a myth, but I would definitely say it is WAAAAAY over-rated, much like sharpness... But this is only by the "gear-oriented" photographers, ones who judge pixel level integrity above light and composition. These are the same photographers that will never shoot stopped down past f11 because they don't want to lose sharpness... But the bottom line is this: An in-focus subject suffering from diffraction will always be infinitely sharper than a subject shot at f8 that's out of the depth of field.

Here's an example I created on the topic a while back. I had to shoot at f18 because of the very near foreground element of the couch corner to the back wall required a very deep depth of field:

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And here's the back wall, where diffraction was evident at f18. But I shot the same scene at f11 to avoid diffraction. But wait! It's sharper at f18! Because it's in focus.

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Always, always shoot at the aperture required to get your subject in focus no matter what that aperture is, diffraction be damned. Your images will always be sharper for it.

Chris M
www.imagineimagery.com

Oct 07, 2008 at 09:11 PM


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