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Author Topic: Do Sensors “Outresolve” Lenses?  (Read 21449 times)

Here to stay

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Do Sensors “Outresolve” Lenses?
« on: October 18, 2014, 07:05:50 pm »

I have a question about this article
Under the " Lens resolution basics" block

In this paragraph
"Lens resolution is limited by diffraction, when you close the diaphragm, and by aberrations, which worsen with focal length and the opening of the diaphragm."
 
Are you say that a lens resolution is limited by both  Diffraction & Aberrations at the same time.
Would this imply that the greatest resolution from a lens would lie at the point where the blur from Diffraction and the blur from Aberrations are the same?
« Last Edit: October 18, 2014, 07:07:25 pm by Here to stay »
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Here to stay

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Re: Do Sensors “Outresolve” Lenses?
« Reply #1 on: October 18, 2014, 07:12:13 pm »

I see now where I should have posted this
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thierrylegros396

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Re: Do Sensors “Outresolve” Lenses?
« Reply #2 on: October 20, 2014, 12:54:00 pm »

If you trust DXO Mark, yes!

Most of the time the center of the Lens is fairly good, but corners can be really poor (example Sony RX100).

Thierry
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michael

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Re: Do Sensors “Outresolve” Lenses?
« Reply #3 on: October 20, 2014, 01:50:52 pm »

There are many forms of lens aberration.

Diffraction is a different type of animal. They are not linked. In fact, some aberrations decrease as a lens is stopped down. Most lenses are at their best about 2 – 3 stops from wide open. Less, and aberrations of various sorts may dominate. more, and diffraction starts.

But, as with all things like this, "It depends".

Michael
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NashvilleMike

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Re: Do Sensors “Outresolve” Lenses?
« Reply #4 on: October 20, 2014, 03:37:01 pm »

Think of it like this:

Diffraction is the maximum potential resolution at any given aperture, no matter what lens, format, or brand. It's a physical limitation, a ceiling, if you will, on how much you can get out of the lens. So if at F/8 diffraction says with red light you can only resolve X, then X is the maximum you'll ever resolve, even if the lens was perfect. (I don't have the time to do the math to tell you what X is at the moment, but you get the idea). Diffraction limits vary with the color (wavelength) of the light.

Lens aberrations tend to vary dependent on the lens. Most lenses tend to correct most aberrations better when they are stopped down a bit. Stop down too far though, and of course you'll be "into" diffraction.

Another way to think of it is that if you just won the lottery and went out and bought the latest exotic Ferrari (or whatever). The car has a maximum top speed - can't do anything about that - it's as fast as that car will go. That's diffraction. Your skill as a driver and/or the road conditions and/or the kinds of tires you're using and/or the weather are factors that will determine how fast YOU will actually be able to drive the car at any given time. It likely won't be at the top speed.

Having said this, don't get paranoid over diffraction. It's there, but it's not a binary thing where if you venture into the land of diffraction your images immediately suck - it's more a gradual thing, apparent in some subject matter more than others, and can be partially mitigated with careful de-convolution sharpening (focusmagic, etc).

Speaking personally, as a D800E owner who owns top tier glass and is rather picky, I realize there is a tradeoff between apertures that are "not in" the diffraction zone and having sufficient DOF for a scene as well as being at an aperture where the aberrations are well corrected and the corners are sharp. I tend to "know" my lenses, and as a general rule tend to shoot the wide angles between F/7.1 and F/9 if I can, and try to stay away from F/11 or beyond unless I need to go there. If I'm in doubt, I'll aperture bracket a scene so I can cover myself with choices.

-m
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Here to stay

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Re: Do Sensors “Outresolve” Lenses?
« Reply #5 on: October 21, 2014, 12:26:36 am »

There are many forms of lens aberration.

Diffraction is a different type of animal. They are not linked. In fact, some aberrations decrease as a lens is stopped down. Most lenses are at their best about 2 – 3 stops from wide open. Less, and aberrations of various sorts may dominate. more, and diffraction starts.

But, as with all things like this, "It depends".

Michael


What I am getting at is the sweet spot at which a lens has the highest resolution is at the Fstop at which you have the least blur due to aberrations and the least blur from diffraction. (the same amount of blur from both
Would look like this
Blur from aberrations ->sweet spot max resolution <- blur from diffraction  
« Last Edit: October 21, 2014, 12:49:13 am by Here to stay »
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Here to stay

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Re: Do Sensors “Outresolve” Lenses?
« Reply #6 on: October 21, 2014, 12:28:50 am »

Think of it like this:

Diffraction is the maximum potential resolution at any given aperture, no matter what lens, format, or brand. It's a physical limitation, a ceiling, if you will, on how much you can get out of the lens. So if at F/8 diffraction says with red light you can only resolve X, then X is the maximum you'll ever resolve, even if the lens was perfect. (I don't have the time to do the math to tell you what X is at the moment, but you get the idea). Diffraction limits vary with the color (wavelength) of the light.

Lens aberrations tend to vary dependent on the lens. Most lenses tend to correct most aberrations better when they are stopped down a bit. Stop down too far though, and of course you'll be "into" diffraction.
This is what I mean the sweet spot between aberrations and diffraction
thank you
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ErikKaffehr

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Re: Do Sensors “Outresolve” Lenses?
« Reply #7 on: October 21, 2014, 01:24:14 am »

Hi,

First class optics are diffraction limited at a useful aperture. The meaning of this is the first airy ring is visible.


In the image above the centrum disk is what is know as the Airy disk, if the lens essentially puts all energy within the Airy disc, the first ring will visible. If significant amount of optical aberrations are present the first ring is obfuscated. Good microscope lenses and astronomical instruments are often diffraction limited at full aperture.

A 3D plot of the airy patter:


A photographic image of the Airy pattern:


The image from Photozone.de below shows MTF 50 values for a Sigma 50/1.4 Art on Canon 5DIII, centrum, edge and corners. You can see that centrum peaks at f/4 (although it is near maximum at f/2) but edges/corners need something like f/4 to reach maximum. Maximum on corners is f/5.6 but centrum looses a tiny bit at f/5.6, due to diffraction.


The example below is also from Photozone, it shows the Canon 50/1.8 a simple standard lens. This lens performs best at f/5.6.



The third example is a 18.5/1.8 for Nikon C1, this is a small sensor camera. Because of the small sensor it needs an excellent lens.The lens is so well corrected that it runs into diffraction limit at f/2.8.


There are many aspects of lenses. MTF is one of those and is generally used in the design phase, but the engineers calculate dozens of MTF curves describing both in focus and out of focus images. Accurate focus is only possible on a single plane, that often is curved. So much of the subject will be more or less out of focus. So out of focus rendition is a very important parameter.

Best regards
Erik



There are many forms of lens aberration.

Diffraction is a different type of animal. They are not linked. In fact, some aberrations decrease as a lens is stopped down. Most lenses are at their best about 2 – 3 stops from wide open. Less, and aberrations of various sorts may dominate. more, and diffraction starts.

But, as with all things like this, "It depends".

Michael

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Ellis Vener

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Re: Do Sensors “Outresolve” Lenses?
« Reply #8 on: October 21, 2014, 12:34:44 pm »

To answer the question in your headline , Do Sensors “Outresolve” Lenses?

Not to be obvious but that depends on the lens and the sensor. Using camera  identical sensor area,  the same individual lens at a given aperture may yield fine results on a12mp sensor, good results on 24mp camera, and only so-so results on a 36mp sensor. it isn't just a matter of pixel count it is also down to the differences in sensor assembly (sensor+ microlenses +anti-aliasing design.

In general  most lenses exhibit their best overall performance  2~3 stops down from wide open - but if the photos you are making  one day  need f/1.4 to work and the next day's project requires f/16 you accept the slightly lower image quality at those apertures so you can make the photographs you need to make.
« Last Edit: October 23, 2014, 12:12:25 pm by Ellis Vener »
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Petrus

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Re: Do Sensors “Outresolve” Lenses?
« Reply #9 on: October 21, 2014, 02:07:19 pm »

Would this imply that the greatest resolution from a lens would lie at the point where the blur from Diffraction and the blur from Aberrations are the same?

Yes.

Aberrations are the greatest at full open and diminish when stopped down. Diffraction is minimal at full open and start to get worse with smaller apertures. Where there two meet is the maximum resolution from this particular lens. Better lenses have this point at larger apertures, worse lenses at higher apertures.
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ErikKaffehr

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Re: Do Sensors “Outresolve” Lenses?
« Reply #10 on: October 21, 2014, 03:04:10 pm »

+1,

Petrus is right.

Well, with some exception astronomical telescopes and microscope lenses are normally sharpest fully open and often don't have aperture.


Best regards
Erik

Yes.

Aberrations are the greatest at full open and diminish when stopped down. Diffraction is minimal at full open and start to get worse with smaller apertures. Where there two meet is the maximum resolution from this particular lens. Better lenses have this point at larger apertures, worse lenses at higher apertures.
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dwswager

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Re: Do Sensors “Outresolve” Lenses?
« Reply #11 on: October 21, 2014, 03:29:26 pm »

In addition to the aberrations and diffraction, add in focus blur.

The answer to your question can be yes, depending on the lens, sensor and technique.  There is a reason the D8X0 cameras are the only 36MP cameras in 35mm sensor size.    In film days Kodak was adamant there was no more than 2400ppi available on film.

From a technical standpoint, lenses perform best stopped down a couple stops from wide open.  In general, f/5.6-f/11 tends to be the sweet spot of lenses.  Diffraction blur tends to begin, depending on the sensor pixel size at about f/7.1 for something like the D7100, DX size, 24MP.  Of course, practical consideration intrude and you make the best image you can by using this information to your best advantage.  The good image you get is always better than the great image you didn't.

There is a misnomer that a lens on low resolution camera can be a good performer, but on a higher resolution camera a weak performer.  This is UNTRUE.  The lens performs identical on all cameras/sensors and at the same image size will look identical, neglecting the impacts imparted by the sensor, electronics and processing algorithms.  Only if you pixel peep will the per pixel sharpness differences be visible and what you are seeing is that the sensor could resolve more than the lens could give.  What this means is a lens that has a resolving power of x while the sensor could handle a resolving power of 2x, the resulting image will still have a resolution of x' and not 2x'.  Basically splitting the resolution across more and more pixels will not increase the resolution.  And the opposite is true.  This is why Kodak thought people scanning film at 9,600ppi were nuts!  What is true is if you want to get the most out of something like the Nikon D810, you need to use lenses that have better resolving abilities with good light and techniques.


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Fine_Art

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Re: Do Sensors “Outresolve” Lenses?
« Reply #12 on: October 21, 2014, 05:01:02 pm »

What I am getting at is the sweet spot at which a lens has the highest resolution is at the Fstop at which you have the least blur due to aberrations and the least blur from diffraction. (the same amount of blur from both
Would look like this
Blur from aberrations ->sweet spot max resolution <- blur from diffraction  


There is still more to it. The sweet spot you refer to may, if using a good lens, be open far enough that part of your subject is out of focus. You cannot just pick the sweet spot then leave the camera there. Chances are the image you want in a landscape for example might need f4 at infinity, f5.6 for far midground, stacks at f8-f11 for the foreground.
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Fine_Art

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Re: Do Sensors “Outresolve” Lenses?
« Reply #13 on: October 21, 2014, 05:12:16 pm »

In addition to the aberrations and diffraction, add in focus blur.

The answer to your question can be yes, depending on the lens, sensor and technique.  There is a reason the D8X0 cameras are the only 36MP cameras in 35mm sensor size.    In film days Kodak was adamant there was no more than 2400ppi available on film.

From a technical standpoint, lenses perform best stopped down a couple stops from wide open.  In general, f/5.6-f/11 tends to be the sweet spot of lenses.  Diffraction blur tends to begin, depending on the sensor pixel size at about f/7.1 for something like the D7100, DX size, 24MP.  Of course, practical consideration intrude and you make the best image you can by using this information to your best advantage.  The good image you get is always better than the great image you didn't.

There is a misnomer that a lens on low resolution camera can be a good performer, but on a higher resolution camera a weak performer.  This is UNTRUE.  The lens performs identical on all cameras/sensors and at the same image size will look identical, neglecting the impacts imparted by the sensor, electronics and processing algorithms.  Only if you pixel peep will the per pixel sharpness differences be visible and what you are seeing is that the sensor could resolve more than the lens could give.  What this means is a lens that has a resolving power of x while the sensor could handle a resolving power of 2x, the resulting image will still have a resolution of x' and not 2x'.  Basically splitting the resolution across more and more pixels will not increase the resolution.  And the opposite is true.  This is why Kodak thought people scanning film at 9,600ppi were nuts!  What is true is if you want to get the most out of something like the Nikon D810, you need to use lenses that have better resolving abilities with good light and techniques.




I have to disagree, I think what you see is the limit of the lens, not what the underutilized sensor is not delivering.

In any event, Erik has convinced me at least, that it is better to have blurry fine pixels than jagged larger ones. Meaning you get more image data even when the pixels are mushy.
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Jim Kasson

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It's not binary
« Reply #14 on: October 21, 2014, 06:15:44 pm »

The title of your post makes it seem that there is a point with decreasing pixel pitch where a sensor "outresolves" a lens, and so further improvement in resolution is possible as the pitch continues to decrease. In fact, over a broad range of pitches, lenses, and lens apertures, both making the lens sharper and making the pixel pitch finer will improve resolution.

Here's an example, from a simulation of a RGGB Bayer-CFA sensor of variable pitch with a beam-splitting AA filter and a model of the Otus 55mm f/1.4.



MTF50 in cycles per picture height for a FF sensor is the vertical axis, pitch in um is coming towards you, and f-stop is from left to right.

If we look down from the top at a "quiver plot", with the arrows pointing in the direction of greatest improvement, and the length of the arrpws proportional to the slope, we can seen that, over much of the aperture range of the lens, the fastest path towards improvement is finer pixel pitch.




Details here and here.

Note that some would call a 2 um sensor used with this lens underutilized, since, on a per-pixel level it is not as sharp as the same lens on a 4 um sensor. Nowever, in cycles per picture height, the finer sensor is sharper.

Jim
« Last Edit: October 21, 2014, 06:21:53 pm by Jim Kasson »
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Here to stay

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Re: It's not binary
« Reply #15 on: October 22, 2014, 01:30:51 am »

The title of your post makes it seem that there is a point with decreasing pixel pitch where a sensor "outresolves" a lens, and so further improvement in resolution is possible as the pitch continues to decrease. In fact, over a broad range of pitches, lenses, and lens apertures, both making the lens sharper and making the pixel pitch finer will improve resolution.



The thread Title was the title of  from this article

http://www.luminous-landscape.com/tutorials/resolution.shtml
And my question had more to do with a specific paragraph within the article

Thank you for all the work you put into this
Would you have any issues if I used your graphs for future reference and do you have a site that I can direct these references to ?
Again thanks

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Jim Kasson

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Re: It's not binary
« Reply #16 on: October 22, 2014, 10:51:14 am »

Thank you for all the work you put into this
Would you have any issues if I used your graphs for future reference and do you have a site that I can direct these references to ?

Use them as you wish. If you post them, please credit me and link to my blog.

The two links above are a good place to start people for this topic, although, if you poke around a little, you'll see that's starting at the middle.

Here's the beginning: http://blog.kasson.com/?p=5720

Jim

dwswager

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Re: Do Sensors “Outresolve” Lenses?
« Reply #17 on: October 22, 2014, 03:52:36 pm »

I have to disagree, I think what you see is the limit of the lens, not what the underutilized sensor is not delivering.

In any event, Erik has convinced me at least, that it is better to have blurry fine pixels than jagged larger ones. Meaning you get more image data even when the pixels are mushy.

Fine_Art,

Not sure what exactly you are disagreeing with, but my point is a point of fact.  A lens performance is independent of the camera sensor onto which it's image circle shines.  If a lens has the resolving power equal to 12 MPs of data (FF Size Sensor), then no matter what sensor reads that FF image circle, you get the same data.  Cutting a pie into 36 slices instead of 12 slices doesn't give you anymore pie!

What a higher resolution capable sensor will do is show you the limited resolving power of the lens, but the lens has not changed it's performance.  and done properly and all else constant, then the print or displayed image will be the same from a 12MP or 36MP sensor.  You could 'upsample' in the camera or post processing, but you still started with the same amount of actual data.  The other benefit of a higher resolution sensor is that it can capture all the data from all lenses less than or equal to it's data saturation point.  Put a better resolving lens on both those sensors and the 12MP starts throwing away data while the 36MP keeps it.

The 1st question I ask my friends when they want to upgrade their camera is why?  Usually it is more MPs.  So if they have a 12MP camera, I ask them "Assuming the format of the picture (2x3) stays the same, what is double the resolution of a 12MP camera?"  They are usually dumbfounded to know it is 48MP!!!


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ErikKaffehr

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Re: Do Sensors “Outresolve” Lenses?
« Reply #18 on: October 22, 2014, 04:22:41 pm »

Nice to hear!

Best regards
Erik

I have to disagree, I think what you see is the limit of the lens, not what the underutilized sensor is not delivering.

In any event, Erik has convinced me at least, that it is better to have blurry fine pixels than jagged larger ones. Meaning you get more image data even when the pixels are mushy.
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Torbjörn Tapani

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Re: Sv: Re: Do Sensors “Outresolve” Lenses?
« Reply #19 on: October 22, 2014, 08:06:24 pm »

Fine_Art,

Not sure what exactly you are disagreeing with, but my point is a point of fact.  A lens performance is independent of the camera sensor onto which it's image circle shines.  If a lens has the resolving power equal to 12 MPs of data (FF Size Sensor), then no matter what sensor reads that FF image circle, you get the same data.  Cutting a pie into 36 slices instead of 12 slices doesn't give you anymore pie!

What a higher resolution capable sensor will do is show you the limited resolving power of the lens, but the lens has not changed it's performance.  and done properly and all else constant, then the print or displayed image will be the same from a 12MP or 36MP sensor.  You could 'upsample' in the camera or post processing, but you still started with the same amount of actual data.  The other benefit of a higher resolution sensor is that it can capture all the data from all lenses less than or equal to it's data saturation point.  Put a better resolving lens on both those sensors and the 12MP starts throwing away data while the 36MP keeps it.

The 1st question I ask my friends when they want to upgrade their camera is why?  Usually it is more MPs.  So if they have a 12MP camera, I ask them "Assuming the format of the picture (2x3) stays the same, what is double the resolution of a 12MP camera?"  They are usually dumbfounded to know it is 48MP!!!
If you find a lens that gives 12 mpix on a 12 mpix sensor you can be certain it will deliver more resolution given a higher mpix sensor.
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