How sharp do you want your photographs? Diffraction revisited (Part Two)

In part one I looked at the effect of diffraction on images made with my 40D.
Now for a fresh look at the subject.

Firstly, we often forget that a less-than-razor-sharp photograph of a good subject is way better than no photograph at all. When you look at many of the great photographs from the past, they are often soft. Not sharp at all. Content always beats sharpness if it has to come down to that.
Secondly, I made these tests from the point of view someone who makes prints. Large ones. You will definitely see the effects of diffraction in print.
But what if you are only interested in projecting your photographs or posting to the web? Remember projectors and screens are low resolution devices: and a two megapixel camera is probably all you need.
You decide. Here are this month’s complete test files from the Canon 5D MkII using the same lens (rendered to 1200×800 jpegs: about the size and quality that you would use for projection and maybe with more detail than you would need for the web).
Click on the thumbnail to open them in a viewer.

Link to canon5dmkIIdiffractiontest
Diffraction Test


Originally I said that I thought the loss of detail at f/16 was recoverable but the loss of detail at f/22 was not. Time to find out. To compare “apples with apples” I first sharpened the f/8 benchmark file using PhotoKit Sharpener:

07F8 original & sharpened


To cut straight to the chase I took the f/22 file and ran it through Topaz InFocus. It uses deconvolution technology to help restore detail. (Photoshop’s Smart Sharpen is also a deconvolution sharpener- you could use that instead if you don’t want to purchase a plug-in). I then ran it through PhotoKit Sharpener at the same setting as for f/8:

08F22 sharpened
Heavens above, I can’t see much difference. Perhaps the f/22 version has a little less contrast. Not difficult to fix. Remember I spent no more than 60 seconds in total on the sharpening. With more time I could do better, but few photographs justify that effort.
Let’s have a look at the f/32 file with the same procedure:

09F32 sharpened
No. It has still had it. Too far gone
Here are crops of the original photos and the sharpened versions together. Click on the thumbnail to open them.


15_F8_F22 sharpened

16_F8_F32 sharpened

The same test with the same lens on my 21 megapixel Canon 5D Mk II had pretty much the same outcome. I also tried it with the 70-300mm f/4-5.6 L IS USM lens. Much the same outcome except this lens is a lot sharper wide open.
Usually if I want more depth of field without losing detail I will take multiple photographs at the sharpest aperture and focus blend them. When I have the time I’ll continue to do this as it gives me more flexibility. But when there is a time restraint f/22 will do just fine. Quite a surprise.
As usual, you need to do your own tests on your own camera to see what works for you.