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Author Topic: Diffraction vs Resolution  (Read 10059 times)

CptZar

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Diffraction vs Resolution
« on: May 07, 2015, 06:50:48 pm »

I remember reading that resolution diminishes diffraction. Meaning that e.g.  a 24 MP sensor at f11 would equal  the diffraction a 36 MP sensor had at f13. So,  with higher resolution you can use smaller apertures, and thus better DOF by maintaining quality.

Is that true, and if how is the actual impact with 36MP and 50 MP sensors? Sensor size being equal.

Cheers

Jan
« Last Edit: May 07, 2015, 06:56:03 pm by CptZar »
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jrsforums

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Re: Diffraction vs Resolution
« Reply #1 on: May 07, 2015, 06:53:45 pm »

I remember reading that resolution diminishes diffraction. Meaning that e.g.  a 24 MP sensor at f11 would equal  the diffraction a 36 MP sensor would have at f13. So,  with higher resolution you can use smaller apertures, and thus better DOF by maintaining quality.

Is that true, and if, how is the actual impact with 36MP and 50 MP sensors?

Cheers

Jan

I think it is just the reverse....sensor size being equal.
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John

CptZar

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Re: Diffraction vs Resolution
« Reply #2 on: May 07, 2015, 06:55:03 pm »

You mean more resolution more diffraction?

jrsforums

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Re: Diffraction vs Resolution
« Reply #3 on: May 07, 2015, 07:32:42 pm »

You mean more resolution more diffraction?

Same sensor size, more resolution = smaller pixel = more diffraction
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John

robdickinson

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Re: Diffraction vs Resolution
« Reply #4 on: May 07, 2015, 08:40:01 pm »

You have it wrong.

Diffraction is the same at the same aperture, it negates resolution

So a 50mp sensor may give you 50mp at f5.6 but only 36mp at f8, 24mp at f13. (guestimates)

So if you shoot at f13 there is little point in using the 50mp sensor

So to get the most out of high resolution sensors you need lenses that are sharp at wider apertures.

With landscapes this means you cant stop down as much without detrimental effects of diffraction.

This may mean more use of tilt and focus stacking.

Note you will never get a worse overall picture with a higher resolution sensor, but it may not give any improvement.
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DeanChriss

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Re: Diffraction vs Resolution
« Reply #5 on: May 07, 2015, 08:40:53 pm »

Diffraction is an optical property of the lens that is the same at any given aperture regardless of the camera resolution. Because the resolution is higher to start with, diffraction starts limiting the camera/lens system resolution sooner (meaning at wider apertures). The diffraction isn't worse, it just becomes apparent at wider apertures. For instance, the "diffraction limited aperture" for a 50MP sensor might be f/6.7 while for a 18MP sensor it might be f/11. That does not mean the 50MP sensor with a lens stopped down to f/11 will produce worse results than the 18MP sensor with the same lens and aperture. That is not the case as diffraction is the same in both cases. OTOH, the 50MP system has lost a lot of its potential resolution to diffraction while the 18MP system hasn't lost any. Some resolution lost to diffraction can be recovered with deconvolution sharpening, though I'm not sure how much.
« Last Edit: May 07, 2015, 08:42:32 pm by DeanChriss »
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Jim Kasson

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Re: Diffraction vs Resolution
« Reply #6 on: May 07, 2015, 10:14:54 pm »

You have it wrong.

Diffraction is the same at the same aperture, it negates resolution

So a 50mp sensor may give you 50mp at f5.6 but only 36mp at f8, 24mp at f13. (guestimates)

So if you shoot at f13 there is little point in using the 50mp sensor

Right general idea, wrong in the specifics:

http://blog.kasson.com/?p=5887

Even at f/12.5 with a diffraction-limited lens, there is a fair amount of improvement to be had going from pixel pitches of 6 um to 3 um. Beyond that, not so much.

Jim

dwswager

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Re: Diffraction vs Resolution
« Reply #7 on: May 07, 2015, 10:45:00 pm »

Diffraction is an optical property of the lens that is the same at any given aperture regardless of the camera resolution. Because the resolution is higher to start with, diffraction starts limiting the camera/lens system resolution sooner (meaning at wider apertures). The diffraction isn't worse, it just becomes apparent at wider apertures. For instance, the "diffraction limited aperture" for a 50MP sensor might be f/6.7 while for a 18MP sensor it might be f/11. That does not mean the 50MP sensor with a lens stopped down to f/11 will produce worse results than the 18MP sensor with the same lens and aperture. That is not the case as diffraction is the same in both cases. OTOH, the 50MP system has lost a lot of its potential resolution to diffraction while the 18MP system hasn't lost any. Some resolution lost to diffraction can be recovered with deconvolution sharpening, though I'm not sure how much.

Thank you!  Finally, some real world useful perspective.

Diffraction losses are real, but the effect have been way, way overblown.  One should always use the best aperture to get the image.  This includes the optical properties of the lens itself, the properties of the imaging system, the artistic vision trying to be captured, etc.  Hence, if one requires f/11 to get the DOF necessary, then accept the diffraction losses.  Yes, tilts and focus stacking are possible options in SOME situations if you have the equipment and time necessary.

I think of optical quality as a precious resource.  Therefore, I never want to squander it, but spend it wisely.  The very good image you get is better than the great image you didn't!
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robdickinson

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Re: Diffraction vs Resolution
« Reply #8 on: May 07, 2015, 11:11:07 pm »

Right general idea, wrong in the specifics:
yeah whatever , I said guestimates.

I think of optical quality as a precious resource.  Therefore, I never want to squander it, but spend it wisely.  The very good image you get is better than the great image you didn't!

aye, there is no point shooting at f5.6 because you avoid diffraction if the shot needs f11 dof.
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Bart_van_der_Wolf

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Re: Diffraction vs Resolution
« Reply #9 on: May 08, 2015, 03:14:59 am »

aye, there is no point shooting at f5.6 because you avoid diffraction if the shot needs f11 dof.

Hi Rob,

That's why some folks use focus-stacking. They use a wider aperture to maintain or increase resolution, less affected by diffraction, and they stack focus for increased DOF.

Cheers,
Bart
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robdickinson

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Re: Diffraction vs Resolution
« Reply #10 on: May 08, 2015, 05:41:57 am »

Hi Rob,

That's why some folks use focus-stacking. They use a wider aperture to maintain or increase resolution, less affected by diffraction, and they stack focus for increased DOF.

Cheers,
Bart


yeah sure thats why I mentioned it in my first post in the thread. But often its not possible.

Thx.
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CptZar

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Re: Diffraction vs Resolution
« Reply #11 on: May 08, 2015, 07:06:31 am »

Not sure if I get it right...but lets say you have a 50MP Camera and a 36MP Camera. Now you shoot both with f16. The 36 MP camera would maybe equal a 24MP camera but the 50MP camera would behave like a 36 MP camera. Now putting pixel peeping aside, in a  practical world, where I would be happy to get a good 36MP shot, the extra pixel wasted by increasing DOF with a smaller f stop might actually be a good investment in all over picture quality.

So from this point of view, even if from a general technical point of view smaller pixel mean more diffraction, using smaller apertures with higher MP sensors would give better quality pictures than using smaller MP sensors with the same aperture. Same sensor size given. This again would mean that one advantage of a 50MP sensor would be to be able to use smaller apertures.
« Last Edit: May 08, 2015, 07:14:03 am by CptZar »
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robdickinson

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Re: Diffraction vs Resolution
« Reply #12 on: May 08, 2015, 07:11:51 am »

No , you have it wrong.

You might get a tinny bit more detail out of the 50mp but really prints from both would look the same.
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spidermike

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Re: Diffraction vs Resolution
« Reply #13 on: May 08, 2015, 07:13:27 am »



So from this point of view, even if from a technical point of view smaller pixel mean more diffraction, the actual result could be better.

And that is where a lot of people get sidetracked - 'diffraction limiting' means just: it limits the benefits of increasing DOF and too many times people seem to be throwing their arms up in horror at the very idea of diffraction causing a degradation of their image quality.
That is where DeanChris comments take a realistic view on it.
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Bart_van_der_Wolf

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Re: Diffraction vs Resolution
« Reply #14 on: May 08, 2015, 07:36:18 am »

Not sure if I get it right...but lets say you have a 50MP Camera and a 36MP Camera. Now you shoot both with f16. The 36 MP camera would maybe equal a 24MP camera but the 50MP camera would behave like a 36 MP camera.

No, this is why it's confusing. Your 36 MP camera does not become or behave like a 24 MP camera.

All that diffraction does is reduce contrast, increasingly so as it approaches the highest spatial frequencies and the narrower the aperture gets, the micro-detail suffers from reduced contrast. A higher MP camera can sample that micro-detail more finely, and thus may extract more detail out of it (which creates more useful data for post-processing).

There is a physical limit beyond which there will be no contrast left due to diffraction, even for high MP cameras, but for the current 50 MP DSLRs that limit is somewhere near f/14. At that limit even lower MP cameras cannot resolve the detail because they lack the resolution, all they see is a bit of blur, but so does the 50 MP camera, just more accurately.

Diffraction itself is not affected by sensor resolution. It is an optical, lens aperture related, phenomenon. All that the sensor does is either resolve the detail there is, or not, and higher MP sensors are better at that.

Cheers,
Bart
« Last Edit: May 08, 2015, 08:24:37 am by BartvanderWolf »
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MarkL

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Re: Diffraction vs Resolution
« Reply #15 on: May 08, 2015, 08:13:54 am »

I'd rather have 'diffraction blur' pixels to make a large print from than invented interpolated up pixels.
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Bart_van_der_Wolf

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Re: Diffraction vs Resolution
« Reply #16 on: May 08, 2015, 08:27:29 am »

I'd rather have 'diffraction blur' pixels to make a large print from than invented interpolated up pixels.

Yes, me too. In addition, there may be some detail that can be recovered with deconvolution sharpening. But then that detail must be resolved first, and that requires more MPixs (to resolve and even over-sample the blur pattern).

Cheers,
Bart
« Last Edit: May 08, 2015, 09:18:24 am by BartvanderWolf »
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Petrus

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Re: Diffraction vs Resolution
« Reply #17 on: May 08, 2015, 08:38:28 am »

At the end of this article https://luminous-landscape.com/do-sensors-aeoeoutresolveae%C2%9D-lenses/ is a table showing the maximum theoretical resolution for different size sensors and wavelengths of light. With the most important wavelength green, 135 size "full frame" sensor would achieve 60 Mpix at f/5.6 and 29 Mpix at f/8. So closing the aperture on 5Ds to smaller than f/7 or so starts to degrade the sharpness of the image.
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Jim Kasson

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Re: Diffraction vs Resolution
« Reply #18 on: May 08, 2015, 08:42:46 am »

At the end of this article https://luminous-landscape.com/do-sensors-aeoeoutresolveae%C2%9D-lenses/ is a table showing the maximum theoretical resolution for different size sensors and wavelengths of light. With the most important wavelength green, 135 size "full frame" sensor would achieve 60 Mpix at f/5.6 and 29 Mpix at f/8. So closing the aperture on 5Ds to smaller than f/7 or so starts to degrade the sharpness of the image.

This table ignores the effects of the Bayer CFA, does it not?

Jim

NashvilleMike

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Re: Diffraction vs Resolution
« Reply #19 on: May 08, 2015, 09:41:19 am »

"I think of optical quality as a precious resource.  Therefore, I never want to squander it, but spend it wisely.  The very good image you get is better than the great image you didn't!"

--> One of the best things I've seen written about this in a long, long time. Perfectly put.

-m
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