This page has the diffraction calculator toward the bottom: http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm
Also note the diffraction calculation is independent of the focal length.
It also needs to be kept in mind that most DOF calculators (and probably diffraction calculators as well) use what is termed 'manufacturer standard' assumption of human visual acuity, whereas the 20/20 vision standard (in the US) is actually about 3x as good as the manufacturer assumption. For example, if I shoot 8x10 at f/22 and focus at 10', most DOF calculators tell that your DOF zone is from 16" to Infinity; using 20/20 vision, DOF zone is from 38" to Infinity.
How does the fact that prints are viewed as closely as the viewer wishes impact on that?
Depends on the film or printing paper too. I cut my teeth on Cibachrome and large format, so what most people consider acceptably sharp I
kinda regard as mush. That doesn't mean prints necessarily have to be that sharp to be esthetically pleasing, but it is a different kind of standard. But there's inherently a lot of BS whenever anyone tries to peg this down to some cut-and-dried formula, just like that "circle of
confusion" and "normal viewing distance" stuff. Diffraction is something to be aware of because it's there. Hope it impacts you and what to do about it all depends. I happen to be someone who needs to keep it in mind rather routinely, but always balanced with other concerns, like desirable depth of field, shutter speed, blah blah.
a circle of confusion is a group of photographwrs sitting around a table talking about depyh of fieldand if you want a deeper understanding,you need to give up photography and study mathematics.
What are your views on this topic? For 35mm format, don't stop the lens further than F8? If need be use a filter to cut the light out? Having seen those who do shoot at F11, F16 or even F22 - is it that bad? There also may be times when one wants a deliberate slow shutter for creative effects, do you simply just pop on a filter?
Most depth of field calculators (and lens DOF markings) assume an 8x10 print viewed at arms length. In that situation you would be hard pressed to see any diffraction up to f/22 from 35mm. However if you print 16x24 the depth of field calculator will be off by a couple of stops and diffraction will be much more visible.
I need to insert a very important additional bit of information to everyone's understanding...
"assume an 8x10 print viewed at arms length" ...by someone with LESS THAN 20/20 visual acuity!
In other words, the average person who has 20/20 vision will see 'this area is blurred!' rather than it appearing to be in 'sharp enough' size of CofC in the enlargement. In this thread I had already brought up the point in Post 22.
a circle of confusion is a group of photographwrs sitting around a table talking about depyh of fieldand if you want a deeper understanding,you need to give up photography and study mathematics.
The thing is that 20/20 visual acuity is measured at 20 feet and says nothing about what one can see at 2 feet.
Hard to say, because the ability to accommodate up close does. If you can't accommodate then the angle of acuity is a mute point.
RalphLambrect said:Some say 8x10 viewed at arms length, some say 8x10 viewed at a foot with someone of less than 20/20 vision.
In the mid-1980s I shot a lot of landscapes at f16 on 35mm, mostly on Nikon lenses. I printed 16 x 12" carefully, with a Nikon enlarging lens. Looking at them recently, all showed clear diffraction issues.
Something that intrigues me is how many modern lenses show their best performance close to wide open, sometimes within half a stop of maximum aperture. I don't know what's changed since the days of manual optics which peaked around f5.6 -f8, perhaps computer design has enabled manufacturers to tweak their lenses for portraiture at the expense of resolution further down the dial.
I agree, but think I the point may have been misunderstood. I'm saying that on test some modern lenses are at their sharpest wide open. The recent Canon 40mm 2.8 and 10-18 zoom are actually at their sharpest at the widest aperture, and sharpness drops as the aperture is closed. That was never previously the case. As you say, two or three stops down was usually the sweet spot, with diffraction kicking in after f8.Many, if not all, modern 35mm lenses are well into diffraction limits at f:16, quite a few at f:11. When I want the maximum detail I try to stay around f:5.6, depending on the lens and film combo.
People who say "diffraction kicks in at f/whatever" are annoying. Diffraction is always there. It doesn't "kick in" at an aperture, at some aperture it becomes the dominant influence on the blur circle. And this has nothing to do with what's capturing the image.
Cropping changes nothing in the image. Now do you understand why your unsubstantiated statement is wrong?
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