# Diffraction Limit Discussion Continuation

Started Feb 21, 2014 | Discussions
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Re: Cutting to the chase.

)Just another Canon shooter wrote:

Jonny Boyd wrote:

Just another Canon shooter wrote:

You will not notice much difference if you open up more, either. All this based on you idea that a 5% drop from, say, 1200 is the same, visually, as 5% drop from 2400, which is a very bold assumption and flat out wrong at moderate viewing sizes.

And where exactly is that assumption?

You are applying 5% threshold for low density sensors and for higher one. This does no prove existence of a limit but let us play that game for a moment. Why fixed percentage? Why not measure it absolute terms? Why not on a log scale?

In this post (Re: Diffraction Limit Discussion Continuation) I said:

If we said that a resolution difference of 0.1% was the limit of perception, then for all practical purposes, peak resolution is indeed a plateau that stretches over several apertures for smaller sensor sizes.

That was just to illustrate a point, rather than an attempt to establish where the actual limit lies.

Elsewhere, in this post (Re: Diffraction Limit Discussion Continuation) I said:

We now need a cut-off point for when a change in resolution will be noticeable. If we assume that a 5% change in resolution is noticeable i.e. when resolution drops below 95% of peak resolution, a difference is noticeable, then we see that diffraction only starts to limit the perceived quality of a print at smaller apertures for lower res sensors.

s = 1, 3, or 10 are never perceptibly limited by diffraction; s = 30 is limited at f/22; s = 100 at f/11; s = 300, 1000, 3000 at f/8.

Again, this is for a purely theoretical setup so real world examples of sensors, lenses, and printers may have more or less pronounced behaviour, depending on actual resolution. My model also assumes that the percentage drop in relative resolution that becomes noticeable would be the same for every absolute resolution. It may be that at higher absolute resolutions a change in relative resolution would be noticeable at a higher or lower resolution. I'm not sure about that one.

Again, it was just giving an example of where the change in perceived resolution could be. It wasn't intended to be a hard and fast claim that our eyes will only notice a drop in resolution of 5%. Not were any claims I was making dependent on that figure.

That hopefully would have been clear in the more recent post (Re: Cutting to the chase.) where I used no numbers and demonstrated that both absolute and relative drop in resolution is less for lower resolution sensors. Hopefully it should be clear from that post, that the claim I'm making about there being a point where resolution is sufficiently low for no change in resolution to be noticed when stopping, is a claim that is not built on any assumptions about the point at which the human eye is unable to see a change in resolution. The only assumption is that such a point exists.

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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'.

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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Re: Diffraction Limit Discussion Continuation

Anders W wrote:

Jonny Boyd wrote:

Yes, the reason I stated: I would rather move forward with the discussion and add to the forum, rather than dig up the past and waste people's time. I'm sure other comemnters would rather read about photography than our personal disagreements, so can we get back the actual discussion?

No problem with that.

I don't know if you realise it, but when you've just spend a whole post pointing the finger and assigning blame, it sounds rather insincere to say at the very end that you have no problem with moving on with discussion rather than digging up the past. I'm tired of that and I'm not inclined to respond any further if that's the way you're going to behave.

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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?

Agreed.

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

Agreed.

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

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?

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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Re: Cutting to the chase.
1

Jonny Boyd wrote:

)Just another Canon shooter wrote:

Jonny Boyd wrote:

Just another Canon shooter wrote:

You will not notice much difference if you open up more, either. All this based on you idea that a 5% drop from, say, 1200 is the same, visually, as 5% drop from 2400, which is a very bold assumption and flat out wrong at moderate viewing sizes.

And where exactly is that assumption?

You are applying 5% threshold for low density sensors and for higher one. This does no prove existence of a limit but let us play that game for a moment. Why fixed percentage? Why not measure it absolute terms? Why not on a log scale?

In this post (Re: Diffraction Limit Discussion Continuation) I said:

If we said that a resolution difference of 0.1% was the limit of perception, then for all practical purposes, peak resolution is indeed a plateau that stretches over several apertures for smaller sensor sizes.

[...]

Again, it was just giving an example of where the change in perceived resolution could be. It wasn't intended to be a hard and fast claim that our eyes will only notice a drop in resolution of 5%. Not were any claims I was making dependent on that figure.

That was not my point. Why do you think that X% drop in resolution, whatever that X is, should be the right way to measure sensitivity? Why not X divided or multiplied by the actual MTF-50 number? Or something else?

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Um...
1

Jonny Boyd wrote:

Great Bustard wrote:

Jonny Boyd wrote:Diffraction causes a decrease in resolution, agreed?

Agreed.

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

Agreed.

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

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?

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.

But how does this make the higher MP sensor more "diffraction limited" than the lower MP sensor?

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.

But you can't see that the higher MP sensor had greater resolution at the peak aperture, so the higher MP sensor isn't being "visibly limited" by diffraction, either, until a much smaller aperture.

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...

But it won't be noticeable -- that's the whole point. The higher MP sensor is resolving better than you can see, so you don't notice the drop in resolution.

...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.

No. Both the high and low MP sensors reached their peak at the same aperture, and the higher MP sensor had higher resolution at every stop, which was beyond what you could see. Thus, if anything, the photo from the higher MP sensor dropped below that visible threshold at a smaller aperture than the photo from the lower MP sensor.

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.

At best what you're trying to say is that the higher MP sensor might go from, say, 3000 lw/ph at it's peak to 2000 lw/ph stopped down to some point, whereas the lower MP sensor might go from 2200 lw/ph to 1900 lw/ph at the same stopped down aperture.

You are then arguing that we would notice a drop in resolution from 3000 lw/ph to 2000 lw/ph, but we wouldn't notice a drop in resolution from 2200 lw/ph to 1900 lw/ph. Thus, you conclude that the lens on the lower MP sensor is "diffraction limited" at a more narrow aperture than the lens on a higher MP sensor.

So, are you trying to define "diffraction limited" as when the lens resolution falls to a particular resolution of its peak value?

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Re: Diffraction Limit Discussion Continuation
2

Jonny Boyd wrote:

Anders W wrote:

Jonny Boyd wrote:

Yes, the reason I stated: I would rather move forward with the discussion and add to the forum, rather than dig up the past and waste people's time. I'm sure other comemnters would rather read about photography than our personal disagreements, so can we get back the actual discussion?

No problem with that.

I don't know if you realise it, but when you've just spend a whole post pointing the finger and assigning blame, it sounds rather insincere to say at the very end that you have no problem with moving on with discussion rather than digging up the past. I'm tired of that and I'm not inclined to respond any further if that's the way you're going to behave.

To end the discussion here is just fine with me. You are not a particularly stimulating discussion partner in substantive terms. On top of that you show bad manners and/or a complete lack of "social intelligence". So now that I know you a bit better, I won't repeat the mistake I made when trying to help you out.

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Yikes!

Jonny Boyd wrote:

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.

I think you've put your finger on it. It seems that a number of your interlocutors have become so invested in (correctly) debunking claims that peak resolution depends on sensor resolution or that lower sensor resolution can combat the effects of diffraction that they can't admit that sensor resolution can have any impact on our ability to perceive the effects of diffraction in actual photographs. If I understand you, you're saying merely that higher resolution sensors will enable us to see more subtle diffraction effects than lower resolution sensors will; a suggestion which I wouldn't have thought to be controversial.

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It seems odd to me...

cmpatti wrote:

Jonny Boyd wrote:

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.

I think you've put your finger on it. It seems that a number of your interlocutors have become so invested in (correctly) debunking claims that peak resolution depends on sensor resolution or that lower sensor resolution can combat the effects of diffraction that they can't admit that sensor resolution can have any impact on our ability to perceive the effects of diffraction in actual photographs. If I understand you, you're saying merely that higher resolution sensors will enable us to see more subtle diffraction effects than lower resolution sensors will; a suggestion which I wouldn't have thought to be controversial.

...that the system that is "diffraction limited" at the wider aperture is the higher resolving system.  For example, if System A is "diffraction limited" at f/4 and System B is "diffraction limited" at f/8, then System A is the higher resolving system, all else equal.

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Re: It seems odd to me...

Great Bustard wrote:

cmpatti wrote:

Jonny Boyd wrote:

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.

I think you've put your finger on it. It seems that a number of your interlocutors have become so invested in (correctly) debunking claims that peak resolution depends on sensor resolution or that lower sensor resolution can combat the effects of diffraction that they can't admit that sensor resolution can have any impact on our ability to perceive the effects of diffraction in actual photographs. If I understand you, you're saying merely that higher resolution sensors will enable us to see more subtle diffraction effects than lower resolution sensors will; a suggestion which I wouldn't have thought to be controversial.

...that the system that is "diffraction limited" at the wider aperture is the higher resolving system. For example, if System A is "diffraction limited" at f/4 and System B is "diffraction limited" at f/8, then System A is the higher resolving system, all else equal.

I'm sorry, but I don't understand why that seems odd.

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Re: It seems odd to me...

cmpatti wrote:

Great Bustard wrote:

cmpatti wrote:

Jonny Boyd wrote:

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.

I think you've put your finger on it. It seems that a number of your interlocutors have become so invested in (correctly) debunking claims that peak resolution depends on sensor resolution or that lower sensor resolution can combat the effects of diffraction that they can't admit that sensor resolution can have any impact on our ability to perceive the effects of diffraction in actual photographs. If I understand you, you're saying merely that higher resolution sensors will enable us to see more subtle diffraction effects than lower resolution sensors will; a suggestion which I wouldn't have thought to be controversial.

...that the system that is "diffraction limited" at the wider aperture is the higher resolving system. For example, if System A is "diffraction limited" at f/4 and System B is "diffraction limited" at f/8, then System A is the higher resolving system, all else equal.

I'm sorry, but I don't understand why that seems odd.

Sorry -- I meant "sounds odd", not "seems odd".  Just sounds like if one system is "diffraction limited" at f/4 then it would not resolve as well as another system that is "diffraction limited" at f/8, 'cause, for me, it's as though it were saying the f/8 "diffraction limited" system keeps getting better and better 'till f/8, whereas the f/4 "diffraction limited" system stops at f/4.

Anyway, that's why it sounds off to me.

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Re: Duck, duck, goose.

Jonny Boyd wrote:

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.

Johnny, for the benefit of everyone: just what is your definition of diffraction limited? A single, short sentence that anyone can understand. Mine is "Resolving power decreases when the lens is stopped down."

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Thing is...

Ulric wrote:

Jonny Boyd wrote:

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.

Johnny, for the benefit of everyone: just what is your definition of diffraction limited? A single, short sentence that anyone can understand. Mine is "Resolving power decreases when the lens is stopped down."

...that's true of all lenses.  It's simply a matter of what aperture the increasing diffraction softening outweighs lessening lens aberrations or, according to Johnny Boyd, what aperture you notice that diffraction is resulting in softer photos (which, of course, also depends tremendously, even primarily, on how large we display the photos, how closely we view them, and our visual acuity).

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Re: Cutting to the chase.
2

Jonny Boyd wrote:

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'.

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?

Life is too short to bother more with this pointless exchange. The nub of it is simple, you set out to 'prove' a mundane and obvious result using extensive calculations based on made-up numbers. That itself was an exercise in futility. My objection to that kind of bogusly quantitative exercise is that the might convince gullible people that there is something of substance in them, because on the surface they look deep and complex, when all they are is an exercise in numerbation (not even measurebation, because there are no genuine measurements involved). As for the result, yes if the pixel count is so small (we discover, about 200k) then you wont see the effects of diffraction or anything else. Every lens becomes perfect. What a great idea.

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Re: It seems odd to me...

Great Bustard wrote:

cmpatti wrote:

Great Bustard wrote:

cmpatti wrote:

Jonny Boyd wrote:

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.

I think you've put your finger on it. It seems that a number of your interlocutors have become so invested in (correctly) debunking claims that peak resolution depends on sensor resolution or that lower sensor resolution can combat the effects of diffraction that they can't admit that sensor resolution can have any impact on our ability to perceive the effects of diffraction in actual photographs. If I understand you, you're saying merely that higher resolution sensors will enable us to see more subtle diffraction effects than lower resolution sensors will; a suggestion which I wouldn't have thought to be controversial.

...that the system that is "diffraction limited" at the wider aperture is the higher resolving system. For example, if System A is "diffraction limited" at f/4 and System B is "diffraction limited" at f/8, then System A is the higher resolving system, all else equal.

I'm sorry, but I don't understand why that seems odd.

Sorry -- I meant "sounds odd", not "seems odd". Just sounds like if one system is "diffraction limited" at f/4 then it would not resolve as well as another system that is "diffraction limited" at f/8, 'cause, for me, it's as though it were saying the f/8 "diffraction limited" system keeps getting better and better 'till f/8, whereas the f/4 "diffraction limited" system stops at f/4.

Anyway, that's why it sounds off to me.

Hmm. I would have thought the opposite.  For example, we usually think that it's a good thing for a lens to be diffraction limited at maximum aperture (as some mFT lenses very nearly are).  Since the term "diffraction limited" simply means that aberrations other than diffraction aren't limiting resolution, you want the system to be "diffraction limited" at the widest aperture possible. Or am I missing something?

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Re: It seems odd to me...

cmpatti wrote:

Great Bustard wrote:

cmpatti wrote:

Great Bustard wrote:

cmpatti wrote:

Jonny Boyd wrote:

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.

I think you've put your finger on it. It seems that a number of your interlocutors have become so invested in (correctly) debunking claims that peak resolution depends on sensor resolution or that lower sensor resolution can combat the effects of diffraction that they can't admit that sensor resolution can have any impact on our ability to perceive the effects of diffraction in actual photographs. If I understand you, you're saying merely that higher resolution sensors will enable us to see more subtle diffraction effects than lower resolution sensors will; a suggestion which I wouldn't have thought to be controversial.

...that the system that is "diffraction limited" at the wider aperture is the higher resolving system. For example, if System A is "diffraction limited" at f/4 and System B is "diffraction limited" at f/8, then System A is the higher resolving system, all else equal.

I'm sorry, but I don't understand why that seems odd.

Sorry -- I meant "sounds odd", not "seems odd". Just sounds like if one system is "diffraction limited" at f/4 then it would not resolve as well as another system that is "diffraction limited" at f/8, 'cause, for me, it's as though it were saying the f/8 "diffraction limited" system keeps getting better and better 'till f/8, whereas the f/4 "diffraction limited" system stops at f/4.

Anyway, that's why it sounds off to me.

Hmm. I would have thought the opposite. For example, we usually think that it's a good thing for a lens to be diffraction limited at maximum aperture (as some mFT lenses very nearly are). Since the term "diffraction limited" simply means that aberrations other than diffraction aren't limiting resolution, you want the system to be "diffraction limited" at the widest aperture possible. Or am I missing something?

I see what you're saying, and, to be honest, I can't disagree.  So, the earlier a lens is "diffraction limited", the better it is, since that means the optical aberrations are small compared to diffraction.  I guess my objection was that "diffraction limited" sounded like "resolution limited".

OK, you've convinced me.Â

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Re: Thing is...

Great Bustard wrote:

Ulric wrote:

Jonny Boyd wrote:

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.

Johnny, for the benefit of everyone: just what is your definition of diffraction limited? A single, short sentence that anyone can understand. Mine is "Resolving power decreases when the lens is stopped down."

...that's true of all lenses. It's simply a matter of what aperture the increasing diffraction softening outweighs lessening lens aberrations or, according to Johnny Boyd, what aperture you notice that diffraction is resulting in softer photos (which, of course, also depends tremendously, even primarily, on how large we display the photos, how closely we view them, and our visual acuity).

It is certainly not true of all lenses that resolving power is at a maximum wide open and decreases as it is stopped down.

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Re: Thing is...

Ulric wrote:

Great Bustard wrote:

Ulric wrote:

Jonny Boyd wrote:

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.

Johnny, for the benefit of everyone: just what is your definition of diffraction limited? A single, short sentence that anyone can understand. Mine is "Resolving power decreases when the lens is stopped down."

...that's true of all lenses. It's simply a matter of what aperture the increasing diffraction softening outweighs lessening lens aberrations or, according to Johnny Boyd, what aperture you notice that diffraction is resulting in softer photos (which, of course, also depends tremendously, even primarily, on how large we display the photos, how closely we view them, and our visual acuity).

It is certainly not true of all lenses that resolving power is at a maximum wide open and decreases as it is stopped down.

You didn't initially say "is at a maximum wide open". So, if you are defining a "diffraction limited lens" as a lens that resolves best wide open, then we are in agreement.

I was just noting that "Resolving power decreases when the lens is stopped down" is true of all lenses once past their peak aperture.  But, for sure, if we add "right from wide open" to the end of that statement, as I said, I agree.

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Re: Thing is...

Great Bustard wrote:

Ulric wrote:

Great Bustard wrote:

Ulric wrote:

Jonny Boyd wrote:

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.

Johnny, for the benefit of everyone: just what is your definition of diffraction limited? A single, short sentence that anyone can understand. Mine is "Resolving power decreases when the lens is stopped down."

...that's true of all lenses. It's simply a matter of what aperture the increasing diffraction softening outweighs lessening lens aberrations or, according to Johnny Boyd, what aperture you notice that diffraction is resulting in softer photos (which, of course, also depends tremendously, even primarily, on how large we display the photos, how closely we view them, and our visual acuity).

It is certainly not true of all lenses that resolving power is at a maximum wide open and decreases as it is stopped down.

You didn't initially say "is at a maximum wide open". So, if you are defining a "diffraction limited lens" as a lens that resolves best wide open, then we are in agreement.

I was just noting that "Resolving power decreases when the lens is stopped down" is true of all lenses once past their peak aperture. But, for sure, if we add "right from wide open" to the end of that statement, as I said, I agree.

Then we don't agree. Or we are talking past each other. It seems that my request to Johnny was unreasonable, there is no way to get one person to explain to another what he means by 'diffraction limit'. I'm sure there will be a third thread to follow up on this one.

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Re: Thing is...
1

Ulric wrote:

Great Bustard wrote:

Ulric wrote:

Great Bustard wrote:

Ulric wrote:

Jonny Boyd wrote:

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.

Johnny, for the benefit of everyone: just what is your definition of diffraction limited? A single, short sentence that anyone can understand. Mine is "Resolving power decreases when the lens is stopped down."

...that's true of all lenses. It's simply a matter of what aperture the increasing diffraction softening outweighs lessening lens aberrations or, according to Johnny Boyd, what aperture you notice that diffraction is resulting in softer photos (which, of course, also depends tremendously, even primarily, on how large we display the photos, how closely we view them, and our visual acuity).

It is certainly not true of all lenses that resolving power is at a maximum wide open and decreases as it is stopped down.

You didn't initially say "is at a maximum wide open". So, if you are defining a "diffraction limited lens" as a lens that resolves best wide open, then we are in agreement.

I was just noting that "Resolving power decreases when the lens is stopped down" is true of all lenses once past their peak aperture. But, for sure, if we add "right from wide open" to the end of that statement, as I said, I agree.

Then we don't agree. Or we are talking past each other. It seems that my request to Johnny was unreasonable, there is no way to get one person to explain to another what he means by 'diffraction limit'. I'm sure there will be a third thread to follow up on this one.

Let me have another go. The effects of diffraction exist right from wide open, and only get worse as you stop down. However, two other effects typically offset this increasing diffraction at the wide end of the aperture: lessening lens aberrations and increasing DOF.

If the entire scene is within the DOF and the diffraction softening outweighs the lens aberrations from wide open, the lens is "diffraction limited". An example of a "diffraction limited" lens would be the Panasonic 7-14 / 4:

http://www.dpreview.com/lensreviews/panasonic_7-14_4_o20/4

On the other hand, if either lessening lens aberrations or increasing DOF outweigh the effects of diffraction softening, then there will be an aperture that results in "optimal resolution", and the lens will be "diffraction limited" past this optimal aperture.

For example, the Panasonic 20 / 1.7 is "diffraction limited" in the center at f/2.2 (DOF permitting), and "diffraction limited" in the corners (or overall) at f/3.3:

http://www.dpreview.com/lensreviews/panasonic_20_1p7_o20/3

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