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.
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.
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:
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.
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.
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?)
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.
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.
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
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?
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.
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.
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.
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.
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.
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.
floris wrote:
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.
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:
