Diffraction Limit Discussion Continuation

Started Feb 21, 2014 | Discussions thread
Jonny Boyd Regular Member • Posts: 105
Re: Duck, duck, goose.

Great Bustard wrote:

Jonny Boyd wrote:

Great Bustard wrote:

Jonny Boyd wrote:

The universal claim I'm disproving is that peak visible resolution always occurs at the same aperture.

You didn't disprove that the peak resolution always occurs at the same aperture, all else equal.

As I've repeatedly said, including in the post you quoted, indeed the very line you quoted, I'm referring to the peak visible resolution, not the peak resolution. There's an important difference.

Did you define the "peak visible resolution"? I mean, since display size, viewing distance, and visual acuity play such important roles in that, I would imagine you discussed them somewhere in your definition.

As I've said elsewhere, I'm not trying to quantify where resolution would visibly drop. I'm merely establishing that both the relative and absolute drop in resolution between apertures is less for a lower resolution sensor, therefore a point will come where that drop is not visible. I don't know when that point would be, or indeed all the factors that would influence, though I imagine it would depend on the ones you've mentioned, along with the lens of course.

At best, you've said that if the resolution is low enough and/or the photo is displayed small enough, there will be a large range of apertures where the loss of resolution either due to lens aberrations for apertures wider than the peak aperture or due to diffraction for apertures more narrow than the peak aperture, will not be noticed,

That's exactly what I've been claiming the whole time in this thread.

Has anyone argued against that? Link and quote, if you'd be so kind.

For some bizarre reason, when I make the claim using one form of words, people agree. When I make it using another form of words, or explain the implications, people disagree. Like in the very same post you wrote.

none of which has anything, whatsoever, to do with being "diffraction limited".

Diffraction causes a decrease in resolution, agreed?


When resolution drops due to stopping down from the peak aperture, that is due to diffraction, agreed?


At the aperture at which diffraction is reducing resolution, you can say that diffraction is limiting the resolution of the final image, agreed?


If resolution appears to be the same at an aperture smaller than the peak aperture then diffraction doesn't become the dominant factor in limiting resolution until later than the peak aperture, agreed?


Therefore, for practical purposes, as far as the eye can see, a system where resolution visibly drops immediately after peak aperture is more limited by diffraction than a system where the visible drop happens later. Agreed?

Not agreed, and am surprised you do not understand this. For example, let's say for a particular display size, viewing distance, and visual acuity, I can resolve 1000 lw/ph. All else equal, the photo from the lower MP sensor will dip below that threshold before the higher MP sensor.

What you're saying is that the lower resolution sensor produces lower resolution images. No kidding, that's what I've always said.

My argument is that for a sufficiently low resolution sensor, an image taken at peak aperture and an image taken at a smaller aperture will have a difference in resolution that is indistinguishable to the naked eye because it is so minor. For practical purposes therefore the perceived resolution is not being limited by diffraction until an even smaller aperture than the actual peak.

In contrast, a higher resolution sensor will exhibit a drop in resolution immediately after the peak aperture which will be greater in relative and absolute terms and be more noticeable, therefore the system is limited by diffraction at an earlier aperture, while (as I have said on numerous occasions) having greater resolution than the lower resolution image.

I get the impression that some people see the words 'diffraction' and 'limit(ed)' in close proximity and freak out without reading what I've written.

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