Diffraction Limit Discussion Continuation

Started Feb 21, 2014 | Discussions thread
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Jonny Boyd
Jonny Boyd Forum Member • Posts: 89
Re: Cutting to the chase.

bobn2 wrote:

Therefore the relative drop in resolution is great for a higher resolution sensor than a lower resolution one.

You do like wasting your own time. I don't think anyone has disputed that would be the case.

You seemed to be highly sceptical of everything I've previously posted.

Therefore the absolute drop is also bigger.

Also probably true.

Then I don't understand why you kept disagreeing with me.

The final implication of this is that as sensor size decreases, the drop in resolution when stepping down constantly decreases.

Pixel count, you probably mean. Best not to complicate things with different sensor sizes at this point.

I meant pixel count, yes.

Given that human eyes have finite ability to distinguish resolution,

That statement is very ill formed, so much so as to be meaningless. What do we mean by 'resolution' and how does one 'distinguish' it? Best to stick with measurable things rather than make unevidenced and undoubtedly simplistic assumptions about human perception. What, for instance, is the role of acuity in all this? Is MTF50 a good model for perceived resolution?

How exactly is it 'ill-informed'? It's a general statement about the ability of the human eye to resolve detail, saying that it has limits. I'm trying to establish what the limits are, merely that they exist. It would be ill-informed to suggest that the human eye has no limit on its ability to perceive detail or differences in resolution.

there will come a point where the resolution at an aperture lower than the peak aperture will be indistinguishable from the resolution at peak aperture to the human eye.

However, I would hazard a guess that is probably true.

Why guess? I did the maths for you. I've outlined the logic. Why guess?

And if you agree, why did you keep trying to tell me I was wrong?

So what? When the image is degraded so much that you can't distinguish between one f-number and another, are we really interested at all?

Without looking at actual examples that's an entirely speculative question. I was merely establishing that the principle that at some point resolution becomes too low to distinguish between the peak aperture and another aperture.

Remember, the decision we're trying to inform here is the trade between DOF and resolution. Just thinking about that trade presupposes a concern for image quality which certainly won't be satisfied by a system so un-diffraction-limited that diffraction has ceased to be a player in resolution at any f-number (and interestingly, this 'diffraction limited' you're talking about has become precisely the reverse of what it means in an astronomical or microscope context).Let's just be clear, as camera with those properties is a dreadful camera, one no serious photographer would want.

I've established a principle, I haven't run numbers to say whether such a camera would always be dreadful. To a extent that's a subjective statement.

That's exactly what I've said with words, illustrated with numbers and charts and have proved with numbers.

You've 'proved' nothing with numbers - working fictitious numbers cannot prove anything. Working fictitious anything can't prove anything.

The numbers illustrated the exact mathematics I did above. If the mathematics you seem to now agree with are correct, then the numbers are examples of what resolution looks like for certain combinations of sensor and lens. If you took a sensors with some of those resolution, and a lens with that resolution, you would get those results, or something close enough since the formula is only a rule of thumb.

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