What does diffraction actually look like?

Started Mar 29, 2012 | Discussions thread
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davidevans1 Senior Member • Posts: 1,423
What does diffraction actually look like?

It's possibly a basic and stupid question, but when I read something along the lines of 'diffraction starts to be noticeable at smaller apertures than F/16' or whatever, how does diffraction degrade the shot?

I'd always assumed it was blurring, and as such I've usually tried to shoot landscapes at around F/11 to F/13. That was until this morning! I went out at dawn, but the light was flat and not contrasty as I'd hoped, so I took some test shots of grass in foreground, trees without leaves, mid distance sky beyond) at various apertures between F/4 and F/22. The lens was 35mm.

Examining the images at 100% I was surprised that I really can't see any increased blurring at the centre or edges at F/18 or F/22.

The blades of grass and tree branches were sharper if anything at these F stops due to the increased depth of field. Unless the answer is that the increased depth of field was sufficient to more than outweigh the increased diffraction.

Maybe I'm looking for the wrong effect, or maybe I should just get on with taking photographs!
Can anyone tell me how noticeable diffraction is in real life situations please?

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