Diffraction Limit Discussion Continuation

Started 10 months ago | Discussions
Great Bustard
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Re: The error in your analysis is...
In reply to knickerhawk, 10 months ago

knickerhawk wrote:

Great Bustard wrote:

knickerhawk wrote:

The prior thread on this interesting if somewhat heated discussion maxxed out before I could post some additional information. I'll leave it to others to address the theoretical differences. I want to return to the issue of evidence. What evidence is there to support the proposition that pixel density does or does not affect the optimal aperture setting for a given sensor size? Some (including the calculator at the Cambridge in Colour website) indicate that the effect of diffraction sets in sooner for sensors with smaller (more) pixels than for sensors with larger (fewer) pixels. Others, including such luminaries as Bobn2, Anders, and Great Bustard, say, "no, no, no" pixel size is not a meaningful factor. So we have a pretty clear-cut difference of opinion that should be relatively easy to resolve with objective lens tests performed on same-sized sensors with differing pixel sizes/densities using the same lens tested at various aperture settings. Right?

I noted several times in the prior thread that DXOMark provides those tests. DXOMark is fairly unique in that most of its lens tests are conducted on a range of cameras. The problem is that it's clunky to find the appropriate data points and plot them. I also noted that in every case that I've looked at, the DXOMark data supports the proposition that pixel size is a non-factor. I've looked at over a dozen lenses tested on several dozen cameras and have yet to find contrary examples. However, it's a big database and I'd encourage others to look as well.

One objection that's been raised is that the DXOMark measurements are too coarse because they're only taken at full f/stop settings. The speculation is that the peak acutance might be occurring somewhere between the measured stops and therefore we can't rely on the DXOMark data. Having looked at enough examples, this struck me as pretty preposterous. Surely, the peaks wouldn't always average out exactly to the same major f-stop setting. Putting that aside, I thought that the data points we do have should be sufficient to infer with some degree a certainty exactly where the peaks occur. I'm certainly no math whiz (far from it!) but I can throw data into an Excel chart and see how the trendlines curve. Below are two examples chosen to illustrate the point. One is M43-based because - after all - that's what this forum is all about; and one is based on an extreme case comparing a 12mp camera (the Nikon D3) to a 36mp camera (the D800). Charts below. Fire away...

...io assuming that all lenses peak at the same aperture:

http://www.josephjamesphotography.com/equivalence/index.htm#diffraction

Diffraction softening is unavoidable at any aperture, and worsens as the lens is stopped down. However, other factors mask the effects of the increasing diffraction softening: the increasing DOF and the lessening lens aberrations. As the DOF increases, more and more of the photo is rendered "in focus", making the photo appear sharper. In addition, as the aperture narrows, the aberrations in the lens lessen since more of the aperture is masked by the aperture blades. For wide apertures, the increasing DOF and lessening lens aberrations far outweigh the effects of diffraction softening. At small apertures, the reverse is true. In the interim (often, but not always, around a two stop interval), the two effects roughly cancel each other out, and the balance point for the edges typically lags behind the balance point for the center by around a stop (the edges usually suffer greater aberrations than the center). In fact, it is not uncommon for diffraction softening to be dominant right from wide open for lenses slower than f/5.6 equivalent on FF, and thus these lenses are sharpest wide open (for the portions of the scene within the DOF, of course).

In other words, there is absolutely no reason, whatsoever, to expect that an 85 / 1.4G would peak at the same aperture as a 25 / 1.4, regardless of the format or pixel size.

I wasn't comparing the Nikkor to the PanaLeica. They're two separate charts with the comparison in each chart between two cameras with the same sensor size but different pixel sizes/counts.

Apologies for the misinterpretation.

I picked the Nikon comparison because of the significant difference in pixel size between the D3 and the D800 and then picked the Oly comparison because this is an M4/3 site.

That's not the error in my analysis. The error is just plain bad math as Golly and Anders have informed me. That's what I get for trying to waltz with the leftbrains here!

Yeah -- I'm not so sure where I left my brain, but I'll find it, hopefully. 

More seriously, sure, more data points are needed for a more definitive conclusion, but if we assume a smooth curve with at most two inflection points, then your graphs show the difference in peak aperture is certainly no more than a stop (although, as discussed, there is no difference for the peak aperture).

What you would want to do is compare the same lens on different sensors. What you will find is that not only is the peak aperture the same regardless of pixel size, but that the higher pixel count sensor will resolve more at every aperture.

Which is what I tried to show with the vertical blue line in each chart.

In other words, pixel size has no effect on diffraction, but pixel count has a definite effect on resolution, although the resolution advantage of more pixels asymptotically vanishes as you stop the lens down.

Understood.

Again, apologies for the misinterpretation.

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bobn2
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Re: Diffraction Limit Discussion Continuation
In reply to Jonny Boyd, 10 months ago

Jonny Boyd wrote:

bobn2 wrote:

Jonny Boyd wrote:

bobn2 wrote:

I think that the semantic argument that this discussion tends to end up in (maybe when the 'peak aperture shifts' people realise that they are wrong) is missing the point of the misinformation and damage to practice that this meme causes. Whatever they wish to decide that they really meant in this abstruse semantic discussion, there are many photographers who look at sites such as CiC, and posts here inspired by it, and end up believing that a low pixel count camera will give them sharper results at small apertures than will a high pixel count camera (absurdities like 'D800 unusable above f/5.6'). While I'm quite prepared to believe that wasn't what they really meant, I'd be more impressed had they made that point in the original posts where they claimed there was a 'diffraction limit'.

I don't recall anyone saying that a low pixel count camera will be sharper than a high res camera (if by sharpness you mean overall image detail).

maybe that hasn't been said explicitly (can't be bothered to go through the whole thread to search) but undoubtedly that is how this bogus 'diffraction limit' gets understood.

The diffraction limit exists, it's just not well understood.

In fact I recall plenty of instances where people have affirmed that although diffraction is visible earlier in high pixel count cameras, they still have more overall detail than a low pixel count camera. What you're saying sounds more like misinformation by suggesting that anyone is making that claim.

I'm basing on what I see understood by it. If we all agree that you still get more detail, what is the point of worrying about this 'diffraction limit' at all?

I don't worry about it personally. But someone asked a question and I found it interesting to think and write about.

It is a genuine concern for those working with telescopes and microscopes more so than ordinary photographers.

But that is a very different 'diffraction limit'. It's not the one that's being talked about here.

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Great Bustard
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Re: Diffraction Limit Discussion Continuation
In reply to Jonny Boyd, 10 months ago

Jonny Boyd wrote:

bobn2 wrote:

Jonny Boyd wrote:

bobn2 wrote:

I think that the semantic argument that this discussion tends to end up in (maybe when the 'peak aperture shifts' people realise that they are wrong) is missing the point of the misinformation and damage to practice that this meme causes. Whatever they wish to decide that they really meant in this abstruse semantic discussion, there are many photographers who look at sites such as CiC, and posts here inspired by it, and end up believing that a low pixel count camera will give them sharper results at small apertures than will a high pixel count camera (absurdities like 'D800 unusable above f/5.6'). While I'm quite prepared to believe that wasn't what they really meant, I'd be more impressed had they made that point in the original posts where they claimed there was a 'diffraction limit'.

I don't recall anyone saying that a low pixel count camera will be sharper than a high res camera (if by sharpness you mean overall image detail).

maybe that hasn't been said explicitly (can't be bothered to go through the whole thread to search) but undoubtedly that is how this bogus 'diffraction limit' gets understood.

The diffraction limit exists, it's just not well understood.

Please define what you mean by "diffraction limit". For reference:

http://www.dpreview.com/forums/post/53154169

Notice also there is no defined 'limit' where the resolution suddenly falls due to diffraction, it is a smooth and even drop-off. The 'limit' is just a bogus idea. McHugh has taken a well defined optical term - a 'diffraction limited' system is one so good that diffraction is the only limit on its performance - turned it inside out and made it into something senseless.

In fact I recall plenty of instances where people have affirmed that although diffraction is visible earlier in high pixel count cameras, they still have more overall detail than a low pixel count camera. What you're saying sounds more like misinformation by suggesting that anyone is making that claim.

I'm basing on what I see understood by it. If we all agree that you still get more detail, what is the point of worrying about this 'diffraction limit' at all?

I don't worry about it personally. But someone asked a question and I found it interesting to think and write about.

It is a genuine concern for those working with telescopes and microscopes more so than ordinary photographers.

The way I see it is that other sources of blur are usually of considerable more importance than diffraction.  The main reason to consider diffraction is to avoid stopping down unnecessarily, such as shooting a landscape at f/16 when everything is easily within the DOF at f/8.

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bobn2
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Re: Diffraction Limit Discussion Continuation
In reply to Great Bustard, 10 months ago

Great Bustard wrote:

The way I see it is that other sources of blur are usually of considerable more importance than diffraction. The main reason to consider diffraction is to avoid stopping down unnecessarily, such as shooting a landscape at f/16 when everything is easily within the DOF at f/8.

Many photographers seem to stop down far more than they need to to get their whole subject within the DOF.

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Great Bustard
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There we have it!
In reply to Jonny Boyd, 10 months ago

Jonny Boyd wrote:

I'm not interested in dissecting the previous discussion. I'd rather go forwards than backwards. What I said before and think is most relevant to the present discussion, is that lower resolution sensors have more of a plateau than a peak, so you get the same resolution effectively at lower apertures as you would at the theoretical peak resolution aperture.

I would agree with this, except I would say "nearly the same resolution" instead of "same resolution".

Therefore a low res sensor isn't diffraction limited at the same aperture as a high res camera.

You really need to defined "diffraction limited". For reference:

http://www.dpreview.com/forums/post/53154169

Notice also there is no defined 'limit' where the resolution suddenly falls due to diffraction, it is a smooth and even drop-off. The 'limit' is just a bogus idea. McHugh has taken a well defined optical term - a 'diffraction limited' system is one so good that diffraction is the only limit on its performance - turned it inside out and made it into something senseless.

More specifically, as I said upthread:

To the uneducated on diffraction, if you say one system is "diffraction limited at f/4" and another system is "diffraction limited at f/5.6", they take it to mean that the system that is "diffraction limited at f/4" will deliver a lower resolution photo at f/5.6 than the system that is "diffraction limited at f/5.6".

Let me illustrate what I mean. Here's a hypothetical lens attached to a number of different hypothetical sensors covering a large range of resolutions. The units for resolution are the same throughout and the table below calculates the systems resolution for each aperture for each sensor.

When we plot the data on a chart, it looks like this:

The highest resolution sensors are virtually indistinguishable from the lens resolution. Below is a table showing what percentage of lens resolution is reached at different apertures by different sensors.

With the low res sensors, resolution is pretty flat across the range. The table below shows the percentage of sensor resolution used at each aperture by each sensor.

If we looked at the numbers with a high enough precision, we would indeed find peak resolution at the same aperture for every lens.

This last sentence, as supported with your charts and graphs, is *exactly* what "we" have been saying.

In practice though, there is no noticeable difference in resolution at any aperture for the lowest resolution sensors.

This would be because the blur from lens aberrations and diffraction are subsumed by the blur of low pixel count.

With high res sensors, you'll gain sharpness by using the peak aperture, but as sensor resolution decreases, you get less and less advantage from the peak aperture and suffer less of a penalty for stopping down.

Indeed:

http://www.josephjamesphotography.com/equivalence/index.htm#diffraction

A common myth is that smaller pixels suffer more from diffraction than larger pixels. On the contrary, for a given sensor size and lens, smaller pixels always result in more detail. That said, as we stop down and the DOF deepens, we reach a point where we begin to lose detail due to diffraction softening. As a consequence, photos made with more pixels will begin to lose their detail advantage earlier and quicker than images made with fewer pixels, but they will always retain more detail. Eventually, the additional detail afforded by the extra pixels becomes trivial (most certainly by f/32 on FF). See here for an excellent example of the effect of pixel size on diffraction softening.

Here's one last table that shows the % of peak resolution that you get at each aperture:

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.

Sure.

Mathematically of course, there is always a peak aperture independent of the sensor. And in practice, the relationship between lens and sensor resolution for a system may be such that no combination of lens and sensor produces a plateau.

The bottom line is there is no reason to fear stopping down to get the necessary DOF with a sensor that has more pixels.  If you are stopping down past the peak aperture, you will not realize the full potential of the higher pixel count sensor, but you will resolve more detail than you would have with the lower pixel count sensor, although that resolution advantage may be trivial, depending on the difference in pixel count and how far you are stopped down.

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Great Bustard
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Re: Diffraction Limit Discussion Continuation
In reply to bobn2, 10 months ago

bobn2 wrote:

Great Bustard wrote:

The way I see it is that other sources of blur are usually of considerable more importance than diffraction. The main reason to consider diffraction is to avoid stopping down unnecessarily, such as shooting a landscape at f/16 when everything is easily within the DOF at f/8.

Many photographers seem to stop down far more than they need to to get their whole subject within the DOF.

I completely agree with this statement, and that is the point that Sergey often raises.

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bobn2
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Re: Diffraction Limit Discussion Continuation
In reply to Great Bustard, 10 months ago

Great Bustard wrote:

bobn2 wrote:

Great Bustard wrote:

The way I see it is that other sources of blur are usually of considerable more importance than diffraction. The main reason to consider diffraction is to avoid stopping down unnecessarily, such as shooting a landscape at f/16 when everything is easily within the DOF at f/8.

Many photographers seem to stop down far more than they need to to get their whole subject within the DOF.

I completely agree with this statement, and that is the point that Sergey often raises.

Partially, it's focussing on the wrong point. Sometimes, just not thinking about how much DOF they actually want.

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Great Bustard
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Re: Diffraction Limit Discussion Continuation
In reply to bobn2, 10 months ago

bobn2 wrote:

Great Bustard wrote:

bobn2 wrote:

Great Bustard wrote:

The way I see it is that other sources of blur are usually of considerable more importance than diffraction. The main reason to consider diffraction is to avoid stopping down unnecessarily, such as shooting a landscape at f/16 when everything is easily within the DOF at f/8.

Many photographers seem to stop down far more than they need to to get their whole subject within the DOF.

I completely agree with this statement, and that is the point that Sergey often raises.

Partially, it's focussing on the wrong point. Sometimes, just not thinking about how much DOF they actually want.

To be honest, I think the problem is more a matter of not applying Equivalence.  That is, they shot landscapes at f/8, f/11, or f/16 on FF, so they do the same with mFT, not thinking that they should instead be shooting f/4, f/5.6, or f/8 on mFT.

Indeed, I even saw one person post a bunch of street photos a while back at f/16 ISO 400 when f/8 ISO 100 would have easily been enough.

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richarddd
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Re: Diffraction Limit Discussion Continuation
In reply to bobn2, 10 months ago

bobn2 wrote:

Great Bustard wrote:

bobn2 wrote:

Great Bustard wrote:

The way I see it is that other sources of blur are usually of considerable more importance than diffraction. The main reason to consider diffraction is to avoid stopping down unnecessarily, such as shooting a landscape at f/16 when everything is easily within the DOF at f/8.

Many photographers seem to stop down far more than they need to to get their whole subject within the DOF.

I completely agree with this statement, and that is the point that Sergey often raises.

Partially, it's focussing on the wrong point. Sometimes, just not thinking about how much DOF they actually want.

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Bob

For a portrait it's easy to choose a focus point, but for deep DOF should one focus at Merklinger's infinity or conventional wisdom's 1/3 (or is it 1/2) of the way or something else? Opinions clearly differ.

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bobn2
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Re: Diffraction Limit Discussion Continuation
In reply to Great Bustard, 10 months ago

Great Bustard wrote:

bobn2 wrote:

Great Bustard wrote:

bobn2 wrote:

Great Bustard wrote:

The way I see it is that other sources of blur are usually of considerable more importance than diffraction. The main reason to consider diffraction is to avoid stopping down unnecessarily, such as shooting a landscape at f/16 when everything is easily within the DOF at f/8.

Many photographers seem to stop down far more than they need to to get their whole subject within the DOF.

I completely agree with this statement, and that is the point that Sergey often raises.

Partially, it's focussing on the wrong point. Sometimes, just not thinking about how much DOF they actually want.

To be honest, I think the problem is more a matter of not applying Equivalence. That is, they shot landscapes at f/8, f/11, or f/16 on FF, so they do the same with mFT, not thinking that they should instead be shooting f/4, f/5.6, or f/8 on mFT.

Indeed, I even saw one person post a bunch of street photos a while back at f/16 ISO 400 when f/8 ISO 100 would have easily been enough.

f/2.8 full frame.

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levimax
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Re: Diffraction Limit Discussion Continuation
In reply to bobn2, 10 months ago

Reading through these two threads has been very enlightening. Previously, when I didn't understand this topic as well as I do now, I was very concerned that the M43 sensor/ system was soon going to be "obsolete" as the pixel density was increased in the future because of diffraction issues. I actually was considering selling my M43 gear and moving to FF because of this issue which would have been a mistake.  Thank You all contributors.

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Great Bustard
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Gotcha beat:
In reply to bobn2, 10 months ago

bobn2 wrote:

Great Bustard wrote:

bobn2 wrote:

Great Bustard wrote:

bobn2 wrote:

Great Bustard wrote:

The way I see it is that other sources of blur are usually of considerable more importance than diffraction. The main reason to consider diffraction is to avoid stopping down unnecessarily, such as shooting a landscape at f/16 when everything is easily within the DOF at f/8.

Many photographers seem to stop down far more than they need to to get their whole subject within the DOF.

I completely agree with this statement, and that is the point that Sergey often raises.

Partially, it's focussing on the wrong point. Sometimes, just not thinking about how much DOF they actually want.

To be honest, I think the problem is more a matter of not applying Equivalence. That is, they shot landscapes at f/8, f/11, or f/16 on FF, so they do the same with mFT, not thinking that they should instead be shooting f/4, f/5.6, or f/8 on mFT.

Indeed, I even saw one person post a bunch of street photos a while back at f/16 ISO 400 when f/8 ISO 100 would have easily been enough.

f/2.8 full frame.

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Bob

Here we are -- FF at f/1.2:

Sharp corner to corner. 

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Great Bustard
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Re: Diffraction Limit Discussion Continuation
In reply to richarddd, 10 months ago

richarddd wrote:

bobn2 wrote:

Great Bustard wrote:

bobn2 wrote:

Great Bustard wrote:

The way I see it is that other sources of blur are usually of considerable more importance than diffraction. The main reason to consider diffraction is to avoid stopping down unnecessarily, such as shooting a landscape at f/16 when everything is easily within the DOF at f/8.

Many photographers seem to stop down far more than they need to to get their whole subject within the DOF.

I completely agree with this statement, and that is the point that Sergey often raises.

Partially, it's focussing on the wrong point. Sometimes, just not thinking about how much DOF they actually want.

For a portrait it's easy to choose a focus point...

The far eye, right?

...but for deep DOF should one focus at Merklinger's infinity or conventional wisdom's 1/3 (or is it 1/2) of the way or something else? Opinions clearly differ.

Whatever gets the portions of the scene you want within the DOF. Truth be told, for a static scene, I shoot a shot with a guess, then check by chimping, and adjust as necessary. Super sophisticated, I know, but I'm smart like that.

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richarddd
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Re: Diffraction Limit Discussion Continuation
In reply to Great Bustard, 10 months ago

Great Bustard wrote:

richarddd wrote:

bobn2 wrote:

Great Bustard wrote:

bobn2 wrote:

Great Bustard wrote:

The way I see it is that other sources of blur are usually of considerable more importance than diffraction. The main reason to consider diffraction is to avoid stopping down unnecessarily, such as shooting a landscape at f/16 when everything is easily within the DOF at f/8.

Many photographers seem to stop down far more than they need to to get their whole subject within the DOF.

I completely agree with this statement, and that is the point that Sergey often raises.

Partially, it's focussing on the wrong point. Sometimes, just not thinking about how much DOF they actually want.

For a portrait it's easy to choose a focus point...

The far eye, right?

...but for deep DOF should one focus at Merklinger's infinity or conventional wisdom's 1/3 (or is it 1/2) of the way or something else? Opinions clearly differ.

Whatever gets the portions of the scene you want within the DOF. Truth be told, for a static scene, I shoot a shot with a guess, then check by chimping, and adjust as necessary. Super sophisticated, I know, but I'm smart like that.

I believe that's the most popular method (based on an earlier thread).   The trend towards cameras with built-in wifi and the omnipresent smart phone (or tablet) could make chimp and adjust even more popular, given that it's easier to review on a screen larger than the typical camera screen.

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Great Bustard
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Excellent!
In reply to levimax, 10 months ago

levimax wrote:

Reading through these two threads has been very enlightening. Previously, when I didn't understand this topic as well as I do now, I was very concerned that the M43 sensor/ system was soon going to be "obsolete" as the pixel density was increased in the future because of diffraction issues. I actually was considering selling my M43 gear and moving to FF because of this issue which would have been a mistake. Thank You all contributors.

I'm very pleased to hear that!

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Mike Davis
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Re: Enlargement factor has been ignored
In reply to Ulric, 10 months ago

Ulric wrote:

Mike Davis wrote:

And that's what's been missing from this discussion - a consideration of the impact of

enlargement factor on diffraction's ability to inhibit a desired print resolution.

I considered that on the very first page of the previous thread.

http://www.dpreview.com/forums/post/53151772

Hey, I missed that.  Good for you!

Actually, pixel pitch can matter even when viewing at enlargement factors far less than 1:1.

Rather than repeat myself, see my post, above.

But yes, you touched on the subject of enlargement factor.  Hooray!  Nobody else seems to care that any comparison that omits specification of the enlargement factor and desired print resolution makes for an apples and orange discussion of either DoF or the impact of diffraction.

Small enlargement factors (had with large sensors and/or small prints) and/or large viewing distances might allow the use of any f-Number available with a given lens and camera, without any fear of diffraction inhibiting a relatively high desired print resolution.  The larger the sensor, the less will be the enlargement factor for any given print size and viewing distance, and thus, the larger the f-Number that can be used before diffraction will begin to inhibit your desired print resolution.

If two sensors are the same size, but one has more pixels than the other, there's some probability that sooner or later, the guy equipped with the higher pixel count is going to make a larger print than the guy who has the lower pixel count on the same size sensor.  Using the higher number of pixels on the same size sensor to produce a larger print causes the Airy disk diameters at the sensor, for any given f-Number, to suffer more magnification in the final print than they would in a smaller print, and thus a greater likelihood of diffraction inhibiting a desired print resolution.  The photographer has to shrink the Airy disks at both the sensor and in the final print (after enlargement), by opening up so that his desired print resolution is not compromised by the larger Airy disks that come with the greater enlargement factor.

Beating the dead horse...

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s_grins
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Re: Enlargement factor has been ignored
In reply to Mike Davis, 10 months ago

Mike Davis wrote:

If two sensors are the same size, but one has more pixels than the other, there's some probability that sooner or later, the guy equipped with the higher pixel count is going to make a larger print than the guy who has the lower pixel count on the same size sensor. Using the higher number of pixels on the same size sensor to produce a larger print causes the Airy disk diameters at the sensor, for any given f-Number, to suffer more magnification in the final print than they would in a smaller print, and thus a greater likelihood of diffraction inhibiting a desired print resolution. The photographer has to shrink the Airy disks at both the sensor and in the final print (after enlargement), by opening up so that his desired print resolution is not compromised by the larger Airy disks that come with the greater enlargement factor.

Beating the dead horse...

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Do you really think that airy disk reveals itself on the print (final of course) as disk?

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Great Bustard
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Re: Enlargement factor has been ignored
In reply to s_grins, 10 months ago

s_grins wrote:

Mike Davis wrote:

If two sensors are the same size, but one has more pixels than the other, there's some probability that sooner or later, the guy equipped with the higher pixel count is going to make a larger print than the guy who has the lower pixel count on the same size sensor. Using the higher number of pixels on the same size sensor to produce a larger print causes the Airy disk diameters at the sensor, for any given f-Number, to suffer more magnification in the final print than they would in a smaller print, and thus a greater likelihood of diffraction inhibiting a desired print resolution. The photographer has to shrink the Airy disks at both the sensor and in the final print (after enlargement), by opening up so that his desired print resolution is not compromised by the larger Airy disks that come with the greater enlargement factor.

Beating the dead horse...

Do you really think that airy disk reveals itself on the print (final of course) as disk?

The Airy Disk "reveals itself" in terms of the blur it introduces into the photo, where the blur is a function of the relative size of the Airy Disk to the photo, not the absolute size:

http://www.josephjamesphotography.com/equivalence/index.htm#diffraction

For the same color and f-ratio, the Airy Disk will have the same diameter, but span a smaller portion of a larger sensor than a smaller sensor, thus resulting in less diffraction softening in the final photo. On the other hand, for the same color and DOF, the Airy Disk spans the same proportion of all sensors, and thus the effect of diffraction softening is the same for all systems at the same DOF.

Let's work an example using green light (λ = 530 nm = 0.00053mm). The diameter of the Airy Disk at f/8 is 2.44 · 0.00053mm·8 = 0.0103mm, and the diameter of the Airy Disk at f/4 is half as much -- 0.0052mm. For FF, the diameter of the Airy Disk represents 0.0103mm / 43.3mm = 0.024% of the sensor diagonal at f/8 and 0.005mm / 21.6mm = 0.012% of the diagonal at f/4. For mFT (4/3), the diameter of the Airy Disk represents 0.0103mm / 21.6mm = 0.048% at f/8 and 0.005mm / 21.6mm = 0.024% at f/4.

Thus, at the same f-ratio, we can see that the diameter of the Airy Disk represents half the proportion of a FF sensor as mFT (4/3), but at the same DOF, the diameter of the Airy Disk represents the same proportion of the sensor. In other words, all systems will suffer the same amount of diffraction softening at the same DOF and display dimensions.

However, the system that began with more resolution will always retain more resolution, but that resolution advantage will asymptotically vanish as the DOF deepens. In absolute terms, the earliest we will notice the effects of diffraction softening is when the diameter of the Airy Disk exceeds that of a pixel (two pixels for a Bayer CFA), but, depending on how large the photo is displayed, we may not notice until the diameter of the Airy Disk is much larger.

Typically, the effects of diffraction softening do not even begin to become apparent until f/11 on FF (f/7.1 on APS-C and f/5.6 on mFT -- 4/3), and start to become strong by f/22 on FF (f/14 on APS-C and f/11 on mFT -- 4/3). By f/32 on FF (f/22 on APS-C, f/16 on mFT -- 4/3) the effects of diffraction softening are so strong that there is little difference in resolution between systems, regardless of the lens, sensor size, or pixel count.

We can now summarize the effects of diffraction softening as follows:

  • There is no "diffraction limit" except when resolution falls to zero.
  • There is a point when the effects of diffraction softening will become the dominant source of blur, and this point will vary from lens to lens as well as where in the frame we are looking (e.g. center vs edges, where the edges typically lag a stop behind the center).
  • All else equal, more pixels will always resolve more detail.
  • All systems suffer the same diffraction softening at the same DOF, but do not necessarily resolve the same detail at the same DOF, as diffraction softening is merely one of many forms of blur (e.g. lens aberrations, motion blur, large pixels, etc.).
  • As the DOF deepens, all systems asymptotically lose detail, and by f/32 on FF (f/22 on APS-C, f/16 on mFT -- 4/3), the differences in resolution between systems is trivial, regardless of the lens, sensor size, or pixel count.
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s_grins
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Re: Enlargement factor has been ignored
In reply to Great Bustard, 10 months ago

Great Bustard wrote:

s_grins wrote:

Mike Davis wrote:

If two sensors are the same size, but one has more pixels than the other, there's some probability that sooner or later, the guy equipped with the higher pixel count is going to make a larger print than the guy who has the lower pixel count on the same size sensor. Using the higher number of pixels on the same size sensor to produce a larger print causes the Airy disk diameters at the sensor, for any given f-Number, to suffer more magnification in the final print than they would in a smaller print, and thus a greater likelihood of diffraction inhibiting a desired print resolution. The photographer has to shrink the Airy disks at both the sensor and in the final print (after enlargement), by opening up so that his desired print resolution is not compromised by the larger Airy disks that come with the greater enlargement factor.

Beating the dead horse...

Do you really think that airy disk reveals itself on the print (final of course) as disk?

The Airy Disk "reveals itself" in terms of the blur it introduces into the photo, where the blur is a function of the relative size of the Airy Disk to the photo, not the absolute size:

http://www.josephjamesphotography.com/equivalence/index.htm#diffraction

For the same color and f-ratio, the Airy Disk will have the same diameter, but span a smaller portion of a larger sensor than a smaller sensor, thus resulting in less diffraction softening in the final photo. On the other hand, for the same color and DOF, the Airy Disk spans the same proportion of all sensors, and thus the effect of diffraction softening is the same for all systems at the same DOF.

Let's work an example using green light (λ = 530 nm = 0.00053mm). The diameter of the Airy Disk at f/8 is 2.44 · 0.00053mm·8 = 0.0103mm, and the diameter of the Airy Disk at f/4 is half as much -- 0.0052mm. For FF, the diameter of the Airy Disk represents 0.0103mm / 43.3mm = 0.024% of the sensor diagonal at f/8 and 0.005mm / 21.6mm = 0.012% of the diagonal at f/4. For mFT (4/3), the diameter of the Airy Disk represents 0.0103mm / 21.6mm = 0.048% at f/8 and 0.005mm / 21.6mm = 0.024% at f/4.

Thus, at the same f-ratio, we can see that the diameter of the Airy Disk represents half the proportion of a FF sensor as mFT (4/3), but at the same DOF, the diameter of the Airy Disk represents the same proportion of the sensor. In other words, all systems will suffer the same amount of diffraction softening at the same DOF and display dimensions.

However, the system that began with more resolution will always retain more resolution, but that resolution advantage will asymptotically vanish as the DOF deepens. In absolute terms, the earliest we will notice the effects of diffraction softening is when the diameter of the Airy Disk exceeds that of a pixel (two pixels for a Bayer CFA), but, depending on how large the photo is displayed, we may not notice until the diameter of the Airy Disk is much larger.

Typically, the effects of diffraction softening do not even begin to become apparent until f/11 on FF (f/7.1 on APS-C and f/5.6 on mFT -- 4/3), and start to become strong by f/22 on FF (f/14 on APS-C and f/11 on mFT -- 4/3). By f/32 on FF (f/22 on APS-C, f/16 on mFT -- 4/3) the effects of diffraction softening are so strong that there is little difference in resolution between systems, regardless of the lens, sensor size, or pixel count.

We can now summarize the effects of diffraction softening as follows:

  • There is no "diffraction limit" except when resolution falls to zero.
  • There is a point when the effects of diffraction softening will become the dominant source of blur, and this point will vary from lens to lens as well as where in the frame we are looking (e.g. center vs edges, where the edges typically lag a stop behind the center).
  • All else equal, more pixels will always resolve more detail.
  • All systems suffer the same diffraction softening at the same DOF, but do not necessarily resolve the same detail at the same DOF, as diffraction softening is merely one of many forms of blur (e.g. lens aberrations, motion blur, large pixels, etc.).
  • As the DOF deepens, all systems asymptotically lose detail, and by f/32 on FF (f/22 on APS-C, f/16 on mFT -- 4/3), the differences in resolution between systems is trivial, regardless of the lens, sensor size, or pixel count.

Thank you for been educated.

But there is one thing that bothers me. Diffraction reveals itself in my camera as a dull image with excessive CA. I did not see any blur caused by diffraction. Probably, I use wrong lens

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Anders W
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Re: Diffraction Limit Discussion Continuation
In reply to Jonny Boyd, 10 months ago

Jonny Boyd wrote:

Anders W wrote:

Jonny Boyd wrote:

there,s nothing there that I hadn't already said to you in other ways.

There most certainly is: The recognition that the point along the aperture range where peak image resolution occurs is independent of sensor resolution.

I never denied that.

Yes you did. Do you want me to look up the specific posts where you denied it or are you going to acknowledge it voluntarily?

I said that at low resolutions it's more of a plateau that a peak, so you effectively get the same resolution at smaller apertures.

No you didn't say that. You said the peak would occur at different apertures depending on sensor resolution (just as Cambridge in Colour). Do you want me to look up the specific posts for you?

Substantively, I have only two comments: That peak sharpness will occur at exactly rather than approximately the same aperture and that "my/our" side is hardly the one to blame for any conceptual or terminological misunderstandings.

Anders, I avoided assigning blame to anyone and put it down to misunderstanding.

Yes I saw that. So I pointed out what was missing.

Don't be in ass in response.

I am not being an ass. You decidedly are by calling me one for absolutely no good reason.

You felt it necessary to assign blame and point fingers when I had hoped the conversation could have a fresh start.

Look! A number of us took time to teach you (I don't apologize for the expression) what things are actually like. We were rewarded by all sorts of insults. Now we are somehow made up as the guilty party just because you not man enough to stand up and say you made a mistake.

If you substantively agree then you'll also agree that when the sensor resolution drops below a certain level, the aperture size won't perceptibly reduce the system resolution in the same way as a system with a sensor resolution similar to the lens resolution. And once you get to a high enough sensor resolution, diffraction overwhelmingly determines system resolution so that the whole system is effectively diffraction limited from wide-open.

What I substantively agree with is the following:

When the sensor resolution is much lower than lens resolution, variations in lens resolution will have but a small impact on image resolution (but still always such that increased lens resolution leads to increased image resolution). When it is the other way around (lens resolution much lower than sensor resolution), variations in lens resolution will have a much stronger impact on image resolution.

I tried to put that to you earlier, but you seemed dismissive of the idea. I'm unclear about whether that is still the case..

Where was I dismissive about the idea as I spelled it out above? Please provide specific references (the post/posts you have in mind and the passage/passages in those posts).

I'm not interested in dissecting the previous discussion.

For pretty obvious reasons.

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