Diffraction Limit

Started Aug 28, 2013 | Discussions thread
olliess Senior Member • Posts: 1,349
Re: Yep.

Dr_Jon wrote:

It's a nightmare reading through all of this and I'm not sure I'm cool on people knocking Airy disks so much (well, if that's what they are doing, with my Astronomical hat on I tend to see them a lot).

There is no such thing as a "diffraction limit" except when the resolution falls to zero.

- well, yes that's true, except it is actually useful to have an idea where diffraction is going to really start killing the sharpness so worth remembering this so-called non-existent limit, while understanding it isn't one you can't bypass (at a cost).

Unfortunately, what we seem to have is people arguing vehemently that because:

1) there is no universal, objective standard for where diffraction "really start[s] killing the sharpness,"

it follows that:

2) that any such attempt is meaningless.

YMMV of course.

More pixels, all else equal, will *always* resolve more detail.

- True, although a chunk of the time it will be to so small a degree you don't care, the rest of the system needs to be in the ball-park. The number of times a friend's D800 out-resolves my 5DmkII are less than you'd think as the pixel effect gets lost in other factors. (He has consumery long lenses, for example)

But the concept of "diminishing returns" confuses people into believing that a higher-resolution sensor will somehow resolve less than a lower-resolution sensor when diffraction effects kick in!

Anyway, I should ask a question - are you unhappy about applying Airy disk maths to either a CoC for viewing a picture of size X at distance Y or using a CoC for the presumed resolution limit of a camera in the 2-3 pixel pitch range (depending on AA filters, de-Bayering algorithms, etc.)?

They are very much unhappy about that; pick through the previous threads if you really want...

Oh, I should say the point being working out when you are likely to really start caring about diffraction effects, but I'll avoid the "L" word. Okay, re-reading that maybe I should have said "Limit" word...

Maybe we can just call it the Subjectively Affected by Diffraction (SAD) limit to stay out of trouble.

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