Diffraction Myth Dispelled

Moderated by: guardian

Visit the FM Store · Image Upload · Buy & Sell
FM Forum Rules
Canon SLRs, primes, and zooms lenses reviews

FM Forums | Canon-mount SLRs | Join Image Upload
1

3 4 5 end

mh2000
Offline
Image Upload: Off

p.2 #1 · Diffraction Myth Dispelled

And just to prove that I am a total geek... I did some quick calculations based on the radius of inscribing circles for a pentagon and octagon... for the 35mm f16 case, and assuming the effective aperture for diffraction effects is based solely on the minimum distance across the aperture, the 35mm lens with 5-blades will be equivalent to an 8-bladed lens of f17.6 (is this really enough to make a significant difference... or is it something else?)

Oct 07, 2008 at 09:45 PM

cwphoto
Offline
Image Upload: Off

p.2 #2 · Diffraction Myth Dispelled

ChrisDM wrote:
IAnd 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.

You may want to rephrase that.

Oct 07, 2008 at 10:34 PM

mh2000
Offline
Image Upload: Off

p.2 #3 · Diffraction Myth Dispelled

hahhh? Makes sense to me.

cwphoto wrote:
ChrisDM wrote:
IAnd 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.

You may want to rephrase that.

Oct 07, 2008 at 10:52 PM

Access
Offline
Image Upload: Off

p.2 #4 · Diffraction Myth Dispelled

What does this have to do with real photo-taking? How often are f/16, f/22 or f/32 actually used in actual photography? I have been taking photos digitally for several years (the original 300D) and the only time I used f/16 was for a macro shot which desired maximum depth-of-field. Even f/8 is something I use very rarely in actual photo-taking. It seems like a lot of people are getting all tied up or bent out of shape about sharpness at aperture ranges that are rarely, if ever, used in real or actual photography.

Oct 07, 2008 at 11:04 PM

floris
Offline
Buy and Sell: On

p.2 #5 · Diffraction Myth Dispelled

Oct 07, 2008 at 11:16 PM

ulrikft
Offline
Image Upload: Off

p.2 #6 · Diffraction Myth Dispelled

According to Dofcalculator, everything between 1m and infinity is in focus on a fullframe at 18mm and f/11 (hyperfocal is 0.97cm), I may be stupid, but when in landscape shooting, or even interiour shooting do you need more dof than that? am I missing something?

Edit:

With a 14mm, the hyperfocal is 0.59cm at f/11.

Oct 07, 2008 at 11:36 PM

danmitchell
Offline
Image Upload: Off

p.2 #7 · Diffraction Myth Dispelled

Access wrote:
What does this have to do with real photo-taking? How often are f/16, f/22 or f/32 actually used in actual photography? I have been taking photos digitally for several years (the original 300D) and the only time I used f/16 was for a macro shot which desired maximum depth-of-field. Even f/8 is something I use very rarely in actual photo-taking. It seems like a lot of people are getting all tied up or bent out of shape about sharpness at aperture ranges that are rarely, if ever, used in real or actual photography.

I have used them in order to get a slower shutter speed in certain situations. (Well, f/16 and f/22 anyway.) In one case I was photographing seascapes and wanted blur from moving water - the longer exposure was more important to me than absolute diffraction-optimized sharpness.

Note that I'm not saying that any aperture is "better" than any other, but that there are situations in which any aperture might be the "best" one for the image you are trying to create.

By the way, in terms of DOF, "everything between 1m and infinity" being in focus is not quite an absolute concept. As you may know, DOF is not a binary concept, as in "your subject is either within it or not." The DOF range is more a less a range in which subjects are _likely_ to be more or less "OOF so little that you may not notice," given certain criteria for measurement that might include format and intended print size. I can say with certainty that at f/16 on FF everything between 1m and infinity will not be sufficiently in focus if you make a large print.

Dan

Oct 07, 2008 at 11:45 PM

mh2000
Offline
Image Upload: Off

p.2 #8 · Diffraction Myth Dispelled

yes, regarding DOF, never trust your end points, they are based on small prints (by todays standards).

Also, not all shots are made with a 24mm lens... not even landscapes.

Oct 08, 2008 at 12:06 AM

n0b0
Online
Image Upload: Off

p.2 #9 · Diffraction Myth Dispelled

If you wanna test for diffraction, try shooting high magnification macro, you'll see the effect better.
Here's a couple of examples.
f/4 and f/5.6
f/8 and f/11

These were shots using natural light so the shutter speed might've exaggerated the effect. I'll do another test later with flash.

Last note, diffraction is not so bad if you don't crop your photos, but if you do, you're in trouble.

Oct 08, 2008 at 01:22 AM

thw2
Offline
Image Upload: Off

p.2 #10 · Diffraction Myth Dispelled

Beni wrote:
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.

If the 1Ds3 is diffraction limited at f/5.6, then ALL the Photozone lens test results which are based on the XT (same pixel density as 1Ds3) are wrong.

Most pixelpeepers have a very poor understanding of diffraction. It may be a real world phenomenon, but its effects are just too exaggerated.

Oct 08, 2008 at 01:33 AM

thw2
Offline
Image Upload: Off

p.2 #11 · Diffraction Myth Dispelled

n0b0 wrote:
If you wanna test for diffraction, try shooting high magnification macro, you'll see the effect better.
Here's a couple of examples.
f/4 and f/5.6
f/8 and f/11

What camera was used?

If you are seeing diffraction in DSLRs at f/4 vs f/5.6, then clearly your test setup is WRONG (misfocusing etc). And I shoot bug macro regularly.

Oct 08, 2008 at 01:37 AM

Pixel Perfect
Offline
Image Upload: On

p.2 #12 · Diffraction Myth Dispelled

Andi Dietrich wrote:
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?

In the macro world it is a real issue and the higher the magnification the smaller the aperture you need to use but you end up with the rule that you need to keep the effective aperture to around f/22 or less, and effective aperture is

f-stop*(M+1)

where M is the magnification. Shoot at 5x you'll need to stick to f/5.6 max otherwise the diffraction induced loss of detail is signifcant.

But for normal shots I agree with Braniac, it's an overstated problem. Take two shots at f/8 and f/22 and initially the f/22 shot will look a lot worse, but if you do some selective sharpening and don't exaggerate noise (shoot at low ISO), the f/22 shot actually can show almost the same level of detail, while offering much more DOF, which may be far more important. Also printing will often mask the very fine detail lost by the diffraction unless you are doing very large prints. It's all intertwined - diffraction, CoC, print size. You could probably get very good 4x6" prints at f/32, but they would look terrible at 16x24".

Shoot at the aperture you need and don't be afraid to stop down. By the same token don't just blindly shoot at f/16 all the time if f/8 will get the job done. Finally look into focus stacking, which while mainly used in macro is starting to get into normal photography. Don't want to shoot at f/22, say you want the subject to be tack sharp from front to back, but still leave the background blurred. Use f/5.6 and take several shots focused at slightly different points on the subject and combine them with tufuse or combineZP. Using f/5.6 means you still have shallow DOF but stacking allows you to selectively enhance DOF over the subject only and avoid small apertures.

Oct 08, 2008 at 02:01 AM

beewee
Offline
Image Upload: Off

p.2 #13 · Diffraction Myth Dispelled

Just something to ponder... diffraction is a function of the size of the light sensitive area for each tiny sensor (photosite) that make up a pixel and not pixel size which is a function of how many pixels per given area.

First, "Pixel size" and photosite sizes are related in that the former cannot be larger than that of the latter. However, the general trend in the past couple years is that although Canon's sensor pixelsize (as a direct function of total number of pixels per given area) has gone up significantly, the actual photosite sizes has stayed relatively the same. This is due to the technological advances in microlens technology and the shrinking of non-photosensitive components on CMOS sensors.

Oct 08, 2008 at 02:13 AM

ChrisDM
Offline
Buy and Sell: On

p.2 #14 · Diffraction Myth Dispelled

cwphoto wrote:
ChrisDM wrote:
IAnd 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.

You may want to rephrase that.

I said that quite clearly.

Oct 08, 2008 at 02:37 AM

ChrisDM
Offline
Buy and Sell: On

p.2 #15 · Diffraction Myth Dispelled

floris wrote:
Access wrote:
What does this have to do with real photo-taking? How often are f/16, f/22 or f/32 actually used in actual photography? I have been taking photos digitally for several years (the original 300D) and the only time I used f/16 was for a macro shot which desired maximum depth-of-field. Even f/8 is something I use very rarely in actual photo-taking. It seems like a lot of people are getting all tied up or bent out of shape about sharpness at aperture ranges that are rarely, if ever, used in real or actual photography.

Have you ever shot any landscapes? I almost always shoot at f/16. Because I need it. Sometimes I need f/18. Of course, if I only need f/11, I'll shoot at f/11.. but rarely do I go below that.

ChrisDM wrote:

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

Nicely said, it really is quite simple in practice

Thank you, yes landscapes are probably the most demanding "stopped down" shooting there is. Here's a recent shot of mine where I had to stop down hard to get the entire scene in focus:

This image is copyrighted by the owner

Chris M
www.imagineimagery.com

Oct 08, 2008 at 02:40 AM

Etadam
Online
Image Upload: On

p.2 #16 · Diffraction Myth Dispelled

Diffraction is not a myth and is calculated pretty easily.
However there are several factors not always taken into account that will lighten the visual effect of diffraction, like the gap between photosites (even with microlenses), the implicit interpolation errors by using a bayer array, the anti-aliasing filter...

And of course, downsizing an image reduces the visible effects of diffraction as it is (roughly) like enlarging the pixel areas.

Would be interesting to have a more formal comparison of 100% crops taken at difference apertures with different pixel sizes (a 5D, 1Ds3 etc...) using top lenses.

Oct 08, 2008 at 03:39 AM

brainiac
Offline
Image Upload: On

p.2 #17 · Diffraction Myth Dispelled

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

Tempest... a tempest in a teacup.

http://en.wikipedia.org/wiki/Tempest_in_a_teapot

Oct 08, 2008 at 10:19 AM

brainiac
Offline
Image Upload: On

p.2 #18 · Diffraction Myth Dispelled

Etadam wrote:
Diffraction is not a myth and is calculated pretty easily.

Nobody on this thread has said that diffraction is a myth. Only that its significance is often exaggerated.

Oct 08, 2008 at 10:25 AM

brainiac
Offline
Image Upload: On

p.2 #19 · Diffraction Myth Dispelled

ChrisDM wrote:
cwphoto wrote:
ChrisDM wrote:
IAnd 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.

You may want to rephrase that.

I said that quite clearly.

Yes, you did, and you are quite right.

Oct 08, 2008 at 10:26 AM

n0b0
Online
Image Upload: Off

p.2 #20 · Diffraction Myth Dispelled

thw2 wrote:
What camera was used?

If you are seeing diffraction in DSLRs at f/4 vs f/5.6, then clearly your test setup is WRONG (misfocusing etc). And I shoot bug macro regularly.

Note that I said "at high magnification". I regularly shoot at f/8 to f/13 when I shoot lifesize, doesn't worry me at all.

In this case, the test images were shot using 450D with MP-E 65mm lens at 5x magnification.

Now at 5x and f/4 the DOF is 0.067mm so the area in focus is very small but you can still see the difference in diffraction between f/4 and f/11 easily.

Is this similar with telephoto? say shooting at 200mm or more? I've never shoot telephoto so I wouldn't know.

Oct 08, 2008 at 10:57 AM

ejmartin
Offline
Image Upload: Off

p.2 #21 · Diffraction Myth Dispelled

I'm in full agreement with Dan that diffraction does not impose a hard cutoff on resolution, rather it's a smooth rolloff which is clear from the formula for it, which states that the amount of blur generated is inversely proportional to the aperture size -- not a hard wall, just a monotonic decrease in resolution in the plane of focus. And as ChrisDM has nicely demonstrated, that can be more than compensated by the increased depth of field rendering more of the image in acceptable focus.

That said, it is fairly easy to see the distinction between f5.6 and f16 in brainiac's OP -- just look at the texture of the wicker chair and the braiding of the blue ropes. The f5.6 images have much more microcontrast and resolution. That resolution difference doesn't mean one should avoid f16 however; it just means that one should realize that f5.6 has higher resolution in the plane of focus, and f16 has larger DOF for a slight loss in resolution at the plane of focus. It's all about tradeoffs, and making the choices that generate the image one desires.

Oct 08, 2008 at 02:06 PM

ejmartin
Offline
Image Upload: Off

p.2 #22 · Diffraction Myth Dispelled

beewee wrote:
Just something to ponder... diffraction is a function of the size of the light sensitive area for each tiny sensor (photosite) that make up a pixel and not pixel size which is a function of how many pixels per given area.

Diffraction does not depend on the proportion of the sensor array that is light sensitive. It is a property of the lens optics, period. The sensor merely records the diffraction-blurred image, to the degree that its resolution allows.

Oct 08, 2008 at 02:09 PM

beewee
Offline
Image Upload: Off

p.2 #23 · Diffraction Myth Dispelled

ejmartin wrote:
The sensor merely records the diffraction-blurred image, to the degree that its resolution allows.

My appologies, I should have probably stated "one's ability to detect the effects of diffraction".

But what you said is exactly the point I'm getting at. You can't detect small amounts of diffraction with large photosites. And so far in past years, we haven't really seen any dramatic decrease in the size of photosites even with the large increases in sensor resolution. Of course, that game will take a turn now since, according to canon, they've effectively gone to "gapless microlenses".

Oct 08, 2008 at 02:25 PM

ejmartin
Offline
Image Upload: Off

p.2 #24 · Diffraction Myth Dispelled

beewee wrote:
ejmartin wrote:
The sensor merely records the diffraction-blurred image, to the degree that its resolution allows.

My appologies, I should have probably stated "one's ability to detect the effects of diffraction".

But what you said is exactly the point I'm getting at. You can't detect small amounts of diffraction with large photosites. And so far in past years, we haven't really seen any dramatic decrease in the size of photosites even with the large increases in sensor resolution. Of course, that game will take a turn now since, according to canon, they've effectively gone to "gapless microlenses".

It's not the size of the photosite that matters for resolution, it's their spacing. Resolution is the precision in detecting a light-to-dark transition, by detecting the light side in one photosite and the dark side (no, not The Dark Side) in the next photosite. So it's the spacing of the photosites that governs the resolution, not the proportion of the photosite's area that is gathering light.

Oct 08, 2008 at 02:47 PM

brainiac
Offline
Image Upload: On

p.2 #25 · Diffraction Myth Dispelled

Thanks to danmitchell and Chris M for good insights into this issue.

Oct 08, 2008 at 02:52 PM


FM Forums \| Canon-mount SLRs \| Join Image Upload 1 2 3 4 5 end