Diffraction Limit Discussion Continuation

Started Feb 21, 2014 | Discussions thread
bobn2 Forum Pro • Posts: 59,045
Re: Diffraction Limit Discussion Continuation

Jonny Boyd wrote:

bobn2 wrote:

Steen Bay wrote:

Anders W wrote:

Jonny Boyd wrote:

I said that at low resolutions it's more of a plateau that a peak, so you effectively get the same resolution at smaller apertures.

No you didn't say that. You said the peak would occur at different apertures depending on sensor resolution (just as Cambridge in Colour). Do you want me to look up the specific posts for you?

Don't think Cambridge in Colour says that. As I read it he's talking about the point at which diffraction will start to become clearly visible at 100% view (with a good lens).

Then he should have been very clear that's what he means.

"Most will find that the f-stop given in the "diffraction limits extinction resolution" field tends to correlate well with the f-stop values where one first starts to see fine detail being softened.

See, he makes no mention of 'clearly visible' nor '100% view'. Moreover, clearly visible at 100% view is a ridiculous condition, who looks at their images 100% view (and in any case, the reproduction size of '100% view' is entirely dependent on the monitor or other medium you use to look at it. As a criterion fro everyday photography, it's useless.

Actually he does:

Use the following calculator to estimate when diffraction begins to influence an image. This only applies for images viewed on-screen at 100%; whether this will be apparent in the final print also depends on viewing distance and print size. To calculate this as well, please visit: diffraction limits and photography.

OK, my apologies to him. He tells people it will be useless. Still, in any case the calculator still doesn't actually tell you 'when diffraction begins to influence an image' because his theory of how diffraction and pixellation interact is just plain wrong.

As evidenced in pretty much every photography forum i existence, people like to pixel-peep, even when minor details at 100% don't all show up in real world viewing.

Liking something and it actually being useful are completely different things.

All other pages of this website therefore use this as the criterion for determining the diffraction-limited aperture."


The calculator says f/7.3 for a 16mp mFT camera and f/4.9 for a 36mp mFT camera. Sounds guite reasonable to me, as a (rather gross) rule of thumb.

What 'sounds reasonable' to you is not generally a good indicator of what is useful.

Yet you were quick to say that CiC is ridiculous because you can't imagine the real world usefulness.

What is the 'real world usefulness'?

Even if we take your condition above ('clearly visible at 100% view'( and then add in the other riders that we'd need to make any sense of it ('assuming 100% view was on a 72 ppi monitor viewed at 60 cm') his calculator still doesn't calculate it.

Actually it does. I refer you again to the quote above, in particular the link to his advanced calculator. Click on the 'Advanced' button and you can input those sorts of parameters.

It doesn't - as I said, the theory on which it operates is wrong.

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