Diffraction Limit Discussion Continuation

Started Feb 21, 2014 | Discussions thread
Jonny Boyd Regular Member • Posts: 105
Re: Cutting to the chase.

bobn2 wrote:

Jonny Boyd wrote:

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.

I've been very sceptical of the methodology of your 'proof','demonstration', whatever it was.

So you say, but without ever articulating what exactly is wrong beyond you not liking the numbers which I plugged into the equation.

What I've said is that it doesn't prove anything, not least the thing you think that it proves, which is that the f-number of the peak moves with pixel size.

Where exactly did I allegedly claim to think that? I've repeatedly said that the actual peak remains constant regardless of pixel size.

My claim, which I'm sick of repeating, is that the aperture after which resolution visibly degrades will, for a sufficiently low resolution sensor, be at a smaller aperture than the peak. Therefore the resolution will appear to be the same across several apertures and the lens will appear to have a resolution plateau instead of a peak, even though in reality it does have a peak, just not one which can be perceived.

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'?

I said and meant 'ill formed', not 'ill informed'.

Sorry, misread that.

It's a general statement about the ability of the human eye to resolve detail, saying that it has limits.

Now you say 'detail', then you said 'resolution'. Which do you mean? Again, when you say 'finite' you are suggesting something quantitative - that 'resolution' or 'detail' could be measured, and there is some result which says that below some limit of this metric, the eyes cannot resolve. So, which do you mean, how is it measured and where is the perceptual evidence o back up what you say?

Why would I need to establish that human vision has limited resolution when you've said in the same post that 'Clearly the human visual system has its limits.'

I'm trying to establish what the limits are, merely that they exist.

You haven't even done that.

Sorry, there should have been a 'not' in there. As in 'I'm not trying to establish what the limits are, merely that they exist.'

Clearly the human visual system has its limits, but so far you have given no information about their nature. I raised the word 'acutance' in a previous post. Is this important? Does the perception of 'detail' or 'resolution' depend on light levels? Does it depend on the type of image? Human perception is a complex thing, and the existence of a simple limit, where you could say that at some point something is invisible based just on an MTF50 measurement, is not a given.

If we're investigating whether pixel size has any effect on when diffraction visibly degrades image resolution, then it makes sense to keep all other factors equal, otherwise you're not just looking at the effect of pixel size.

Different viewing conditions would I imagine have an affect on when a difference in resolution becomes noticeable, but I'm not trying to quantify where that would happen for any particular condition, merely that it would happen at some point.

It would be ill-informed to suggest that the human eye has no limit on its ability to perceive detail or differences in resolution.

No-one said 'ill informed'.

I said ill-informed and meant it.

But it is indeed 'ill informed' to assume that human perception has very simple limits that can be predicted with a metric like MTF50, especially when there can be such variety in viewing conditions, which have not been stated.

I refer you to my previous comments.

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?

The maths was done based on fictitious figures,

Where are the 'fictitious' figures in this post Re: Cutting to the chase.?

the logic was fallacious

You're asserting that, but not backing it up.

  • therefore your exercised shows nothing. That doesn't mean that some of the results you were purporting to show don't stack up in the real world.

Ah, it's just a remarkable coincidence, is it?

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

I told you that your experiment was bogus beginning to end, see above about its relationship to real world results.

You said you didn't like it, but you could never actually point out anything wrong. When I used numbers, you couldn't show how they were unrepresentative of reality. When I didn't use numbers, you couldn't highlight any problems with my working.

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.

Take it as a hypothetical. Does your running the numbers show you just how low a pixel count a camera would need to take diffraction out of the picture?

That would depend on the lens, the viewing conditions, the quality of a person's eye-sight and so on. Establishing where the limit would be isn't simple.

Is that a pixel count most serious photographers would be content with?

What is a 'serious' photographer, and where did I ever mention them? Are they the only ones who matter? Do I know all their needs?

I was merely establishing that the principle that at some point resolution becomes too low to distinguish between the peak aperture and another aperture.

You just had to say it - that isn't controversial.

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,

Not at all. The 'principle' you established - that you can reduce pixel count to the point where diffraction is the least of your worries - was pretty obvious to everyone. But that wasn't the 'priciple' you purported to be establishing, which was that there would be a 'plateau' which would effectively move the peak resolution. You never established that.

The peak resolution doesn't 'move.' The point at which resolution visibly degrades moves. That's what I keep saying, and you keep saying I'm wrong while simultaneously agreeing that 'at some point resolution becomes too low to distinguish between the peak aperture and another aperture.' It's an oddly contradictory view you seem to hold.

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

To an extent Let's go back to your own numbers. We seem to get a pretty flat line when the 'sensor resolution' is 30. 30 what, you don't say, but we can make an estimate, because the lens resolution for the lens at f/22 is 60 of whatever they are. f/22 in practice is usually diffraction limited and seems to give an MTF50 of 30 lp/mm on lenstip's methodology (http://www.lenstip.com/392.4-Lens_review-Olympus_M.Zuiko_Digital_12-40_mm_f_2.8_ED_PRO_Image_resolution.html). So '60' means 30 lp/mm, which means that '30' means '15'. So we're talking about 15 lp/mm or 30 pixels/mm, or 200k pixels on a mFT sensor. Do you think that is a resolution anyone here is seriously going to aim for?

I wouldn't presume to know that needs of anyone. Nor was I attempting to establish whether the resolution would be at such a low point that no-one would want to use it. Having said that, the resolution would be sufficient for web use.

There are of course other problems with the example you've taken.

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,

I don't agree that the 'mathematics' are 'correct'.

Really? I gave the mathematics in this post: Re: Cutting to the chase.

Then in the next post (Re: Cutting to the chase.), immediately after the mathematics, you said

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

As i said, you used a sometimes useful approximate formula,

Is it useful in this case or not?

ran some unrealistic numbers with it,

I've asked you quite a few times to tell me what exactly is unrealistic, but all you seem to do is repeat your assertion.

and came out with a bogusly quantitative result

I never claimed that the result represented a real situation in any quantitative sense, merely that it illustrated qualitatively what happens.

which did no more than show what was obvious before you did it.

Yet here you are, still arguing.

You wasted your time and brought nothing new to the discussion. The fact that I agree that the obvious was all along obvious in no way validates your 'mathematics'.

So the mathematics from I derive the obvious are wrong, but the obvious is right? And because I stated the obvious, you decided to argue that I was wrong. Okay…

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.

200kP is your measure of quality?

I don't recall every saying that.

Why, exactly, do you have an interest in mFT equipment?

So after lecturing me about not contributing anything to the discussion, you make a comment like that. Do you realise that you come across as rather hostile, rude, condescending, and unwelcoming? Really, what was the need for a comment like that?

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