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Resolution, noise and print size

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Iuvenis

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Imatest say that MTF50 is a good way to test the sharpness of different cameras and lenses. This is something that lens testing websites have taken to heart, as they normally use this measure.

This is useful for those testing lenses and cameras. It is also useful for people to work out how large they can print - in good light - from particular lens and camera combinations, while still preserving details on close viewing. Imatest specifically provide guidance on the issue of print size here, suggesting for example that resolution of 150lw per inch is a good standard to aim for: http://www.imatest.com/docs/sharpness/

In reality, however, the resolution of fine detail is greatly influenced by noise. A large number of my photographs (and I am sure I am not alone in this) are taken in low light conditions. In such conditions, I cannot print nearly as large as I can for photographs taken in good light, as the prints are either spoiled by visible noise, or smudged detail caused by noise reduction.

Based on my experience (Fuji XT2), I run out of resolution on my camera and lenses when printing 24 inches wide, however good my technique and however favourable the conditions. The results can still look good from a distance, but don't stand up to very close inspection. That seems to match the Imatest recommendations. However, to my surprise, noise doesn't seem to be a particular issue at this size, up to iso 800. That is despite noise being clearly visible when pixel peeping at that setting.

At iso 3200 and 6400 on the other hand, just two stops higher, I can only make decent medium sized prints, before noise becomes the limiting factor. The fine detail is just obscured. Prints at iso 12800 or more only look good at very small sizes - so small, I rarely bother to use this setting at all.

However, this is subjective stuff. What I cannot see is any way of relating resolution, noise levels and print size in any objective way.

Imatest mention noise and noise reduction a lot on their site, but mainly in the context of avoiding it influencing the test results. I learnt today (from another thread) that you can't work out the effect of noise by rerunning MTF tests in low light conditions, as MTF50 is not significantly affected by noise, though noise does make it harder to get an accurate reading: http://mtfmapper.blogspot.co.uk/2013/01/effects-of-iso-on-mtf50-measurements.htm

Is there a way to conceptualise the impact of noise on resolution and print size? Or is it just a question of personal experience?

Is noise just a factor impacting resolution of detail, or does it act like an absolute ceiling on resolution? Based on my experience, it seems to have a slight impact up to a certain point, and then a rapidly increasing impact thereafter, to a point noise is the only important factor, but I am interested why it seems to have this effect.

Will a higher pixel count camera still resolve more than a lower pixel count camera with the same sensor size and lens when light is sufficiently low? Or does the per area noise 'drown out' the fine detail to the same extent on each?

Is there a point at which noise means high resolution lenses cease to be an advantage?
 
Iuvenis said:
Imatest say that MTF50 [SNIP all that stuff about MTF]
Click to expand...
MTF is an outdated and old concept. Not a modern one. So lets just not talk about it. :-)
Iuvenis said:
Is there a way to conceptualise the impact of noise on resolution and print size? Or is it just a question of personal experience?
Click to expand...
Yes, there is. One can quantify the effect of noise in many situations.
Iuvenis said:
Is noise just a factor impacting resolution of detail, or does it act like an absolute ceiling on resolution?
Click to expand...
If there were no noise then one can get unlimited resolution - in theory! Despite all the slogans that one might hear that 'information can't be created', indeed, in theory, information can be created as the imaging process puts certain restrictions on the structure and properties of the images so produced that any missing information due to optical limits can be recovered. However, just in theory, mostly. As in practise noise is a killer and doesn't let one recover that info. Also, while theory might say it is possible to recover info that was destroyed by optical limits, an actual algorithm to recover such detail would require stability that perhaps may not always be granted.

--
Dj Joofa
http://www.djjoofa.com
 
Last edited:
Iuvenis said:
However, this is subjective stuff. What I cannot see is any way of relating resolution, noise levels and print size in any objective way.
Click to expand...
Hmm. Just thinking out loud, but what about a method that simply compares a captured image to an expected image. Something like this:

1. Take a checkerboard target, like the one used by OpenCV to perform camera calibration. The idea is that this will give us fairly accurate locations for the corners of the checkerboard squares, so we can locate a particular part of our test chart fairly accurately within the image.

2. Instead of keeping the interior of the checkerboard squares black or white, we embed concentric circles (white/black alternation, like a USAF1951 bars) inside each square. We can vary the width of the white/black circular bands (constant line width in a given square, but different widths in different checkerboard squares) to sample different spatial resolutions, again, similar to USAF1951. We make sure to have multiple copies of each of particular resolution (white/black band width) so that we can obtain a statistical sample of each resolution under the observed image noise. The whole chart would look something like this:



A quick mock-up. In a real chart, the white/black band width would be different in most of the squares, and we can also place the circular pattern in the white squares, of course.
A quick mock-up. In a real chart, the white/black band width would be different in most of the squares, and we can also place the circular pattern in the white squares, of course.



3. Because we know what the expected contents of each checkerboard square is, and we know their locations within the image (from the corners), we can render the expected contents of each square, a bit like texture mapping into each square (the mtf_generate_rectangle tool in MTF Mapper already contains the code for doing this). Then we can compare the observed contents of the square with the expected contents using a suitable similarity metric. Something like normalized cross correlation or SSIM.

4. We can then plot the similarity metric vs resolution (white/black band widths) to obtain a visualization of how the captured image compares to the expected image at various resolutions, in effect automating the interpretation of a USAF1950 or "trumpet" style chart. I would expect the similarity metric to "bottom out" roughly at the highest resolution that can be resolved, but this is just speculation at this point.



Like I said, these are just a few quick thoughts on how we can design a test chart and algorithm to estimate resolution in a way that would be sensitive to noise.



Any thoughts?



-Frans
 
Iuvenis said:
Imatest say that MTF50 is a good way to test the sharpness of different cameras and lenses. This is something that lens testing websites have taken to heart, as they normally use this measure.

This is useful for those testing lenses and cameras. It is also useful for people to work out how large they can print - in good light - from particular lens and camera combinations, while still preserving details on close viewing. Imatest specifically provide guidance on the issue of print size here, suggesting for example that resolution of 150lw per inch is a good standard to aim for: http://www.imatest.com/docs/sharpness/

In reality, however, the resolution of fine detail is greatly influenced by noise. A large number of my photographs (and I am sure I am not alone in this) are taken in low light conditions. In such conditions, I cannot print nearly as large as I can for photographs taken in good light, as the prints are either spoiled by visible noise, or smudged detail caused by noise reduction.

Based on my experience (Fuji XT2), I run out of resolution on my camera and lenses when printing 24 inches wide, however good my technique and however favourable the conditions. The results can still look good from a distance, but don't stand up to very close inspection. That seems to match the Imatest recommendations. However, to my surprise, noise doesn't seem to be a particular issue at this size, up to iso 800. That is despite noise being clearly visible when pixel peeping at that setting.

At iso 3200 and 6400 on the other hand, just two stops higher, I can only make decent medium sized prints, before noise becomes the limiting factor. The fine detail is just obscured. Prints at iso 12800 or more only look good at very small sizes - so small, I rarely bother to use this setting at all.

However, this is subjective stuff. What I cannot see is any way of relating resolution, noise levels and print size in any objective way.

Imatest mention noise and noise reduction a lot on their site, but mainly in the context of avoiding it influencing the test results. I learnt today (from another thread) that you can't work out the effect of noise by rerunning MTF tests in low light conditions, as MTF50 is not significantly affected by noise, though noise does make it harder to get an accurate reading: http://mtfmapper.blogspot.co.uk/2013/01/effects-of-iso-on-mtf50-measurements.htm

Is there a way to conceptualise the impact of noise on resolution and print size? Or is it just a question of personal experience?

Is noise just a factor impacting resolution of detail, or does it act like an absolute ceiling on resolution? Based on my experience, it seems to have a slight impact up to a certain point, and then a rapidly increasing impact thereafter, to a point noise is the only important factor, but I am interested why it seems to have this effect.

Will a higher pixel count camera still resolve more than a lower pixel count camera with the same sensor size and lens when light is sufficiently low? Or does the per area noise 'drown out' the fine detail to the same extent on each?

Is there a point at which noise means high resolution lenses cease to be an advantage?
Click to expand...
The difficult bit is that the impact of noise on detail is progressive. It starts on small low contrast detail that's already at the limit of visibility. So MTF50 is not going to be very different at ISO200 or ISO400.

But if you SHARPEN the image, you need low contrast detail above MTF50 to increase sharpness, but all you end up sharpening is low contrast detail that is already mostly buried in the noise. So you are sharpening noise.

Resolution is determined by pixels, but the ISO limit is determined by sensor size. In other words, a 32MP has twice as many pixels as a 16MP image, but if we print at 36X24 instead of 24X16, we double the area and increase noise visibility by a stop. If you decide your full frame noise limit is ISO400 at 24X16, then it is ISO 200 at 36X24.

Or, you could increase linear resolution by 1.42X and print at 24X16 to improve sharpness, but to see the full benefit of the extra sharpness, you would have to reduce ISO by 1 stop. Once again, you are limited to ISO200.

The easiest thing is to determine your own subjective limit - say APSC at ISO200 for 24X16 and 16MP, and adjust accordingly.
 
[No message]
 
57even said:
Iuvenis said:
Imatest say that MTF50 is a good way to test the sharpness of different cameras and lenses. This is something that lens testing websites have taken to heart, as they normally use this measure.

This is useful for those testing lenses and cameras. It is also useful for people to work out how large they can print - in good light - from particular lens and camera combinations, while still preserving details on close viewing. Imatest specifically provide guidance on the issue of print size here, suggesting for example that resolution of 150lw per inch is a good standard to aim for: http://www.imatest.com/docs/sharpness/

In reality, however, the resolution of fine detail is greatly influenced by noise. A large number of my photographs (and I am sure I am not alone in this) are taken in low light conditions. In such conditions, I cannot print nearly as large as I can for photographs taken in good light, as the prints are either spoiled by visible noise, or smudged detail caused by noise reduction.

Based on my experience (Fuji XT2), I run out of resolution on my camera and lenses when printing 24 inches wide, however good my technique and however favourable the conditions. The results can still look good from a distance, but don't stand up to very close inspection. That seems to match the Imatest recommendations. However, to my surprise, noise doesn't seem to be a particular issue at this size, up to iso 800. That is despite noise being clearly visible when pixel peeping at that setting.

At iso 3200 and 6400 on the other hand, just two stops higher, I can only make decent medium sized prints, before noise becomes the limiting factor. The fine detail is just obscured. Prints at iso 12800 or more only look good at very small sizes - so small, I rarely bother to use this setting at all.

However, this is subjective stuff. What I cannot see is any way of relating resolution, noise levels and print size in any objective way.

Imatest mention noise and noise reduction a lot on their site, but mainly in the context of avoiding it influencing the test results. I learnt today (from another thread) that you can't work out the effect of noise by rerunning MTF tests in low light conditions, as MTF50 is not significantly affected by noise, though noise does make it harder to get an accurate reading: http://mtfmapper.blogspot.co.uk/2013/01/effects-of-iso-on-mtf50-measurements.htm

Is there a way to conceptualise the impact of noise on resolution and print size? Or is it just a question of personal experience?

Is noise just a factor impacting resolution of detail, or does it act like an absolute ceiling on resolution? Based on my experience, it seems to have a slight impact up to a certain point, and then a rapidly increasing impact thereafter, to a point noise is the only important factor, but I am interested why it seems to have this effect.

Will a higher pixel count camera still resolve more than a lower pixel count camera with the same sensor size and lens when light is sufficiently low? Or does the per area noise 'drown out' the fine detail to the same extent on each?

Is there a point at which noise means high resolution lenses cease to be an advantage?
Click to expand...
The difficult bit is that the impact of noise on detail is progressive. It starts on small low contrast detail that's already at the limit of visibility. So MTF50 is not going to be very different at ISO200 or ISO400.

But if you SHARPEN the image, you need low contrast detail above MTF50 to increase sharpness, but all you end up sharpening is low contrast detail that is already mostly buried in the noise. So you are sharpening noise.
Click to expand...
Member said:
Resolution is determined by pixels, but the ISO limit is determined by sensor size. In other words, a 32MP has twice as many pixels as a 16MP image, but if we print at 36X24 instead of 24X16, we double the area and increase noise visibility by a stop. If you decide your full frame noise limit is ISO400 at 24X16, then it is ISO 200 at 36X24.
Click to expand...
It's a good point that noise scales based on print area, whereas resolution is normally measured in linear fashion. That would explain my experience that iso 800 is OK at 24 inches wide, but iso 3200 needs to be about 12 inches wide (2 stops less light, 1/4 of the print area).

Also, it would explain why there comes a point where noise simply ceases to be an issue at all, and only resolution matters.

Your figures are much more conservative than mine, but based on my rule of thumb that iso 800 is Ok at 24 inches wide, iso 200 images could be printed at 48 inches wide and show similar noise levels. However, at this stage, resolution is limiting the print size, not noise.
Member said:
Or, you could increase linear resolution by 1.42X and print at 24X16 to improve sharpness, but to see the full benefit of the extra sharpness, you would have to reduce ISO by 1 stop. Once again, you are limited to ISO200.
Click to expand...
Member said:
The easiest thing is to determine your own subjective limit - say APSC at ISO200 for 24X16 and 16MP, and adjust accordingly.
Click to expand...
That's more or less what I've done. It's interesting that there doesn't seem to be much by way of objective testing the effect of noise on resolution, however.
Member said:
--
Reporter: "Mr Gandhi, what do you think of Western Civilisation?"
Mahatma Gandhi: "I think it would be a very good idea!"
Click to expand...
 
True - I wouldn't miss an opportunity to print larger than 24 inches if I could, even if it wouldn't look great close up. It's a bit expensive printing at that size, though, and it is nice when people look at your prints close up to see the details.
 
I like this suggestion, as although the effect of noise on resolution is plain enough, it would be better if we could measure its effect. However, I'm afraid that I don't have the expertise to tell if your suggestion would work.
 
Iuvenis said:
True - I wouldn't miss an opportunity to print larger than 24 inches if I could, even if it wouldn't look great close up. It's a bit expensive printing at that size, though, and it is nice when people look at your prints close up to see the details.
Click to expand...
I sometimes think it would be funny to define a photographer's depth of field or PDOF, which would define how close a photographer can stick his nose up to a print before seeing out of focus blur.

But I've noticed that art buyers in galleries will look at images from a reasonable distance, viewing them whole and entire by standing back from them. Only photographers seem to view images up close.
 
Iuvenis said:
Imatest say that MTF50 is a good way to test the sharpness of different cameras and lenses. This is something that lens testing websites have taken to heart, as they normally use this measure.
Click to expand...
I would note that MTF50 is a product or measure used "only" by the photographic, and perhaps videographic communities. There is a single conference proceeding paper ( https://www.spiedigitallibrary.org/...uality-Criteria/10.1117/12.948802.short?SSO=1 ) that introduces it; no other literature. It has not been shown to:

1. Correlate with subjective evaluation, as is e.g. SQF

2. Serve as a good single number proxy for the full MTF curve except in special circumstances; i.e., the MTF curve is not linear or linear-ish.

3. Relate to the term "resolution," which is usually intended as short for "limiting resolution." MTF20 ~ MTF0 would be more appropriate for that (depends how much noise you can tolerate).

Most lens testing websites use Imatest's platform, and MTF50 is the default in imatest. Since most are photographers first and optical, electrical, etc, engineers a distant second if at all, it is unsurprising they do not depart from the default.

I do not know why Imatest uses MTF-50. The proceedings paper I linked above [I can give you a PDF copy if you want] is not widely known, and Norman Koren was not an optical engineer, so it is a bit unlikely he was rooting through the SPIE library. It's possible he independently decided on it, or he found this, or there is another source I have missed for MTF-50.

Here's a set of noise free images of concentric squares at various contrast levels. Do you find the 50% image to be particularly stand-out or significant?
Iuvenis said:
In reality, however, the resolution of fine detail is greatly influenced by noise.
Click to expand...
(n.b., I am not an expert on noise)

Depending on the type and magnitude of noise as well as image contents, the impact could be completely mitigated. For an "average photographic scene" this may not be the case.
Iuvenis said:
Is there a way to conceptualise the impact of noise on resolution and print size? Or is it just a question of personal experience?
Click to expand...
May respond to this later -- flying/traveling tomorrow
Iuvenis said:
Is noise just a factor impacting resolution of detail, or does it act like an absolute ceiling on resolution? Based on my experience, it seems to have a slight impact up to a certain point, and then a rapidly increasing impact thereafter, to a point noise is the only important factor, but I am interested why it seems to have this effect.
Click to expand...
Noise is in some sense a linear thing for some types of cameras (Sony-style sensor); it increases linearly with ISO (which is just a form of gain) except for a kink around ISO 640 on cameras with Aptina DR-pix technology.

If at base ISO, the image is super clean, say 70dB SNR, you may not notice a degradation until the image has < 20dB SNR or some number. After that it would rapidly corrupt. You may imagine this is kind of a log curve thing; 3dB SNR Is pretty bad, 6dB twice as good, 9dB better but not twice as good, etc...
Iuvenis said:
Will a higher pixel count camera still resolve more than a lower pixel count camera with the same sensor size and lens when light is sufficiently low? Or does the per area noise 'drown out' the fine detail to the same extent on each?
Click to expand...
Depends a lot on the camera and technology I think.
Iuvenis said:
Is there a point at which noise means high resolution lenses cease to be an advantage?
Click to expand...
The sharper the underlying image, the more you can blur it with NR before the details are totally lost.
 
Joofa said:
Iuvenis said:
Imatest say that MTF50 [SNIP all that stuff about MTF]
Click to expand...
MTF is an outdated and old concept. Not a modern one. So lets just not talk about it. :-)
Click to expand...
Beating your drum... provide an alternative.
Joofa said:
Joofa said:
Is there a way to conceptualise the impact of noise on resolution and print size? Or is it just a question of personal experience?
Click to expand...
Yes, there is. One can quantify the effect of noise in many situations.
Click to expand...
Example? Anything real to add?
Joofa said:
Joofa said:
Is noise just a factor impacting resolution of detail, or does it act like an absolute ceiling on resolution?
Click to expand...
If there were no noise then one can get unlimited resolution - in theory!
Click to expand...
Very limited theory.
Joofa said:
Despite all the slogans that one might hear that 'information can't be created', indeed, in theory, information can be created as the imaging process puts certain restrictions on the structure and properties of the images so produced that any missing information due to optical limits can be recovered. However, just in theory, mostly. As in practise noise is a killer and doesn't let one recover that info. Also, while theory might say it is possible to recover info that was destroyed by optical limits, an actual algorithm to recover such detail would require stability that perhaps may not always be granted.
Click to expand...
Yadda yadda, analytic continuation blah blah.

I posit that if you already know what is in the picture (a req. for analytic continuation), why bother taking the picture? Why not just simulate it if you didn't need more "real world" data?

Or do you propose we fit some "special" (not in the mathematical sense) functions like sinc or a bessel basis set, etc, to the image data in spatial or fourier domain (oops, you don't like fourier)? That involves some highly restrictive assumptions about what is in the image, and probably blows up in practice even more often than a noise limitation would impose.

I invite you to post a paper (by you, anyone, I don't care) on this analytic continuation magic so that we can weigh its merits on more than an "I promise it works awesome" basis. A book with specific page/chapter ref would be fine, too.
 
AiryDiscus said:
I do not know why Imatest uses MTF-50. The proceedings paper I linked above [I can give you a PDF copy if you want] is not widely known, and Norman Koren was not an optical engineer, so it is a bit unlikely he was rooting through the SPIE library. It's possible he independently decided on it, or he found this, or there is another source I have missed for MTF-50.
Click to expand...
For a filter designer, the -6dB point (20*log10(1/2)) is a standard way of describing cutoff frequency.

-h
 
AiryDiscus said:
Joofa said:
Iuvenis said:
Imatest say that MTF50 [SNIP all that stuff about MTF]
Click to expand...
MTF is an outdated and old concept. Not a modern one. So lets just not talk about it. :-)
Click to expand...
Beating your drum... provide an alternative.
Click to expand...
I have provided a number of different alternatives in the past as free software plugins for Photoshop, ImageJ, etc. For e.g., this thread from 2011 about an ImageJ plugin:

https://www.dpreview.com/forums/post/38200511

And, some comments from a user who used it on some of his experiments:

https://www.dpreview.com/forums/post/38205278
Member said:
Member said:
Member said:
Is there a way to conceptualise the impact of noise on resolution and print size? Or is it just a question of personal experience?
Click to expand...
Yes, there is. One can quantify the effect of noise in many situations.
Click to expand...
Example? Anything real to add?
Click to expand...
That will be another discussion. But, the short answer is yes, it is possible.
Member said:
Member said:
Member said:
Is noise just a factor impacting resolution of detail, or does it act like an absolute ceiling on resolution?
Click to expand...
If there were no noise then one can get unlimited resolution - in theory!
Click to expand...
Very limited theory.
Member said:
Despite all the slogans that one might hear that 'information can't be created', indeed, in theory, information can be created as the imaging process puts certain restrictions on the structure and properties of the images so produced that any missing information due to optical limits can be recovered. However, just in theory, mostly. As in practise noise is a killer and doesn't let one recover that info. Also, while theory might say it is possible to recover info that was destroyed by optical limits, an actual algorithm to recover such detail would require stability that perhaps may not always be granted.
Click to expand...
Yadda yadda, analytic continuation blah blah.
Click to expand...
I did not even mention analytic continuation above.
Member said:
I posit that if you already know what is in the picture (a req. for analytic continuation), why bother taking the picture? Why not just simulate it if you didn't need more "real world" data?

Or do you propose we fit some "special" (not in the mathematical sense) functions like sinc or a bessel basis set, etc, to the image data in spatial or fourier domain (oops, you don't like fourier)? That involves some highly restrictive assumptions about what is in the image, and probably blows up in practice even more often than a noise limitation would impose.

I invite you to post a paper (by you, anyone, I don't care) on this analytic continuation magic so that we can weigh its merits on more than an "I promise it works awesome" basis. A book with specific page/chapter ref would be fine, too.
Click to expand...
Here is a link from a past discussion, on which thread you were also participating, where I posted some papers from known experts that have used analytic continuation for image restoration:

https://www.dpreview.com/forums/post/60274251

Also, it appears that you have not read Goodman's famous Fourier Optics text very carefully. Goodman himself talks about these methods (including analytic continuation) in section 6.6 (2nd ed.) entitled "Resolution Beyond the Classical Diffraction Limit".

--
Dj Joofa
http://www.djjoofa.com
 
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Ah, so JIMD or whatever. This magic, unpublished noone-is-able-to-see-the-formula metric. Which we should take at face value like DxO?

One person saying it seems to be more sensitive than other options in ImageJ is not a strong sales pitch. E.g. the slanted-edge MTF plugin for ImageJ is not very good, so MTF from ImageJ is not a good measure of MTF, and if poor metrics e.g. MTF50 are pulled from the measurement, the sensitivity is even worse.
 
hjulenissen said:
AiryDiscus said:
I do not know why Imatest uses MTF-50. The proceedings paper I linked above [I can give you a PDF copy if you want] is not widely known, and Norman Koren was not an optical engineer, so it is a bit unlikely he was rooting through the SPIE library. It's possible he independently decided on it, or he found this, or there is another source I have missed for MTF-50.
Click to expand...
For a filter designer, the -6dB point (20*log10(1/2)) is a standard way of describing cutoff frequency.

-h
Click to expand...
Unfortunately, in optics it is not. "-14 to -20 dB" is the norm (10% to 20% modulation).
 
AiryDiscus said:
Ah, so JIMD or whatever. This magic, unpublished noone-is-able-to-see-the-formula metric. Which we should take at face value like DxO?
Click to expand...
You brought JIMD into discussion. I did not even mention it originally.
Member said:
One person saying it seems to be more sensitive than other options in ImageJ is not a strong sales pitch.
Click to expand...
It is not just one person using it. I just provided a link to the comments of one person from years ago. But, apparently you were not satisfied.
Member said:
E.g. the slanted-edge MTF plugin for ImageJ is not very good,
Click to expand...
Who cares about the slanted edge method when it can't let you do things of practical nature that are needed and are important: :-)

http://forum.luminous-landscape.com/index.php?topic=107311.msg893452#msg893452

BTW, there are several plugins in the general JIMD umbrella. Another, related one, JISR measured sharpness between two images as a ratio:

http://forum.luminous-landscape.com/index.php?topic=60585.msg489070#msg489070
Member said:
so MTF from ImageJ is not a good measure of MTF,
Click to expand...
Which has nothing to do with my ImageJ plugin.
Member said:
and if poor metrics e.g. MTF50 are pulled from the measurement, the sensitivity is even worse.
Click to expand...
I'm not talking about MTF50 here. I know you don't like the author of ImaTest and MTF50. But, he has created a software that a large number of people use for good purpose.

--

Dj Joofa
http://www.djjoofa.com
 
Last edited:
hjulenissen said:
AiryDiscus said:
I do not know why Imatest uses MTF-50. The proceedings paper I linked above [I can give you a PDF copy if you want] is not widely known, and Norman Koren was not an optical engineer, so it is a bit unlikely he was rooting through the SPIE library. It's possible he independently decided on it, or he found this, or there is another source I have missed for MTF-50.
Click to expand...
For a filter designer, the -6dB point (20*log10(1/2)) is a standard way of describing cutoff frequency.
Click to expand...
Then something has changed. When I was designing filters, it was the 3 db point. That's half power, but not half voltage.

Jim
 
AiryDiscus said:
3. Relate to the term "resolution," which is usually intended as short for "limiting resolution." MTF20 ~ MTF0 would be more appropriate for that (depends how much noise you can tolerate).
Click to expand...
When testing at the system level, I find that MTF50 often approaches, and sometimes exceeds, Nyquist. MTF30 is much worse (or better, depending on how you look at it) in that respect. MTF20 would of course be even worse (or better).

I question the utility of a system metric for something that is not beneficial to the photographer. Of course, if you're must measuring the lens, that's different.

Jim
 
JimKasson said:
AiryDiscus said:
3. Relate to the term "resolution," which is usually intended as short for "limiting resolution." MTF20 ~ MTF0 would be more appropriate for that (depends how much noise you can tolerate).
Click to expand...
When testing at the system level, I find that MTF50 often approaches, and sometimes exceeds, Nyquist. MTF30 is much worse (or better, depending on how you look at it) in that respect. MTF20 would of course be even worse (or better).

I question the utility of a system metric for something that is not beneficial to the photographer. Of course, if you're must measuring the lens, that's different.

Jim
Click to expand...
 
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