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Author Topic: Do Sensors “Outresolve” Lenses?  (Read 21447 times)

dwswager

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Re:
« Reply #80 on: October 25, 2014, 04:37:13 pm »

Hi,

I don't really see your point, but I feel that very good prints can be made from small MP files. Early on, 135 on good film was considered to be around 6MP, but it was found that 3 MP digital was actually good match for 135 film.

Now, my normal print size is A2, and I don't feel that 6 MP is good enough for that. But I don't see a lot of difference between 12 MP and 24 MP at that size. So, I would say that I (personally) need something like between 12 MP and 24 MP for a very good print. That difference from 6 MP to 24 MP is worth a journey to Iceland for me.

Personally, I would never buy a D3. I don't shoot high ISO or 10 FPS. I shoot on tripod, with MLU and at 50 ISO. So with my shooting habits a low MP high FPS camera simply make no sense.

Some folks are shooting high ISOs on free hand, that is another game, not about resolution but about getting that image.

Best regards
Erik


Oh, so we are in violent agreement!  It was the phone cam comment that threw me.  I've taken few photos with my phone as I find the quality and especially the ability to post process on the phone is so limiting, at least to me.  The only benefit to it is immediacy and ease.

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Re: It's not binary
« Reply #81 on: October 26, 2014, 02:12:34 am »



I have run MTF tests in pixel sizes from 9 my to 3.8 my, and lens performance essentially always peaks at the same aprtures, but with smaller pixels we get more resolution at a given MTF (which often is choosen at 50%).

So what I would say, the advantage of smaller pixels is better definition of whatever the lens renders, and that applies to any somewhat well corrected lens.

Best regards
Erik
thank you for the response

Sorry for the late follow up its been a busy end of the week here
I first noticed an earlier peak when using a MTP mapper for AF & catzeye calibration. I hadn’t noticed it from generation to generation of camera bodies but rather going from a 6mp  to a 24mp camera. It started with a 300 2.8 and I had noticed it on my 24mp, normally I would set my focus calibration for F5.6 my most used range to help combat focus shift problems with sigma. I later ran quick MTP F8 to 2.8 and found that I peaked somewhat earlier than my first 6mp cropped body. This peaking I also noticed had a greater effect with targets further away and with longer FLs  when setting up focus for the common distance I shoot at. For example with a 50mm 1.4 when using a target 4-7m away there was very little difference, once I started setting the focus targets 8-10m  away I started to see this peak.
Now that I shoot mainly FF It would be interesting to see some data going from 12-36mp and see if  this is a figment of my imagination {  Blur from resolution-limited sensor-> highest resolution (highest Airy Disk edge contrast that the sensor can detect) <- blur from diffraction      } or not.

 I had a renewed interest in this when I first seen this Lensrentals charts




When we take a look at the 50 1.8 G with 5.92 µm µm pixel D3x

to a 50mm 1.8 G 3.39 µm pixel V1




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Jim Kasson

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Re: It's not binary
« Reply #82 on: October 26, 2014, 12:17:23 pm »

This peaking I also noticed had a greater effect with targets further away and with longer FLs  when setting up focus for the common distance I shoot at. For example with a 50mm 1.4 when using a target 4-7m away there was very little difference, once I started setting the focus targets 8-10m  away I started to see this peak.

Moving the target further away has the effect of making the slanted edge sharper, and therefore the SFR software capable of finer discrimination. Try the test with a target that is cut from thin mylar rather than printed and see if the effect still occurs.

It could also be that the lens is better corrected for farther subject distance.

Jim

Fine_Art

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Re: It's not binary
« Reply #83 on: October 26, 2014, 03:12:44 pm »

Moving the target further away has the effect of making the slanted edge sharper, and therefore the SFR software capable of finer discrimination. Try the test with a target that is cut from thin mylar rather than printed and see if the effect still occurs.

It could also be that the lens is better corrected for farther subject distance.

Jim

Can you explain how that works a bit more? I have the Sigma 35 Art, that I think has the opposite. It can be incredible within 30ft, it seems average at infinity.
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Jim Kasson

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Re: It's not binary
« Reply #84 on: October 26, 2014, 03:42:22 pm »

Can you explain how that works a bit more? I have the Sigma 35 Art, that I think has the opposite. It can be incredible within 30ft, it seems average at infinity.

Are you talking about slanted-edge testing, or in general? If it's the latter, your Sigma might not be well-corrected at infinity, although, in my experience, that's rarer than not being corrected for close distances.

Jim

Bart_van_der_Wolf

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Re: It's not binary
« Reply #85 on: October 26, 2014, 03:44:56 pm »

Moving the target further away has the effect of making the slanted edge sharper, and therefore the SFR software capable of finer discrimination. Try the test with a target that is cut from thin mylar rather than printed and see if the effect still occurs.

Hi Jim,

That's correct, but it could also indicate that the target was not printed with a high enough resolution (e.g. 300 or 360 PPI instead of 600 PPI, or 720 PPI with 'finest detail'). Also, shooting from a distance of 50x the focal length would produce an image magnification on the sensor of 1:49, or a factor of 0.02041, which should reduce a printed edge transition that's sharp enough to exceed the resolution of the lens alone.

Quote
It could also be that the lens is better corrected for farther subject distance.

That could also play a role. It usually is recommended to test at something close to the actual shooting distance, although that may create some practical challenges, especially for long focal lengths. I think it's usually safe to test at 25-50x focal length if the target is of good quality (600, or 720 PPI with 'finest detail') , otherwise 100x FL should suffice (e.g. for C-print targets). Of course accurate focusing is critical, and harder than one may expect.

It would be interesting to see how e.g. the Otus responds to shooting a slanted edge from different distances.

Cheers,
Bart
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ErikKaffehr

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Re: It's not binary
« Reply #86 on: October 26, 2014, 03:45:16 pm »

Can it focus correctly at infinity?

Best regards
Erik

Are you talking about slanted-edge testing, or in general? If it's the latter, your Sigma might not be well-corrected at infinity, although, in my experience, that's rarer than not being corrected for close distances.

Jim
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Re: It's not binary
« Reply #87 on: October 27, 2014, 01:29:41 am »

Moving the target further away has the effect of making the slanted edge sharper, and therefore the SFR software capable of finer discrimination. Try the test with a target that is cut from thin mylar rather than printed and see if the effect still occurs.

It could also be that the lens is better corrected for farther subject distance.

Jim
What I am using is a thin mylar like material with adhesive that is mounted to flat white plastic board. I was using a printed chart from the web and found that up close that it was the resolution causing me problems.  

If this was due to being better corrected for farther subjects would not the peak still be held at the same F stop.
I think part of the problem is when testing up close that the software is least accurate and the further away the software can detect the peak as I describe below 

Why I bring this up is that I see a peak when using a 5d classic and several lenses that they would peak at lets say F7 then moving over to a higher resolution camera like a 7d that they would peak earlier on in the F-stop. this would suggest to me that we indeed see a peak at the point where the resolution of the sensor can more accurately map the location of the Airy disks. And not where the just lens peaks but rather where the system peaks (lens and pixel size)  Its not a large peak but never the less its there.

 
« Last Edit: October 27, 2014, 01:46:22 am by Here to stay »
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bjanes

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Re: It's not binary
« Reply #88 on: October 27, 2014, 08:10:35 am »

Moving the target further away has the effect of making the slanted edge sharper, and therefore the SFR software capable of finer discrimination. Try the test with a target that is cut from thin mylar rather than printed and see if the effect still occurs.

It could also be that the lens is better corrected for farther subject distance.

Jim

Jim,

That is an interesting suggestion. Where can one obtain this mylar?

Bill
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Fine_Art

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Re: It's not binary
« Reply #89 on: October 27, 2014, 11:12:56 am »

Can it focus correctly at infinity?

Best regards
Erik


I better test that. It is very close if it is hitting the limits.
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Jim Kasson

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Re: It's not binary
« Reply #90 on: October 27, 2014, 11:52:11 am »

That is an interesting suggestion. Where can one obtain this mylar?

My suggestion is a piece of completely exposed, then developed B&W 4x5 film (T-Max 400 (TMY) would be my first choice), taped at a slight angle emulsion side out to a piece of white, smooth matte paper, such as the back of a piece of priniting paper (Oriental Seagull VC would go with the film, but I use Exhibition Fiber), using black gaffer's tape. Be sure to light the target so that the 7-mil (?) thickness of the film doesn't cast a shadow on the backing paper. Estar is Kodak's name for something very much like Mylar. To keep the film close to the plane of the paper, you can get the gaffer tape close to the edge, but if any fibers stick over the edge, it will confuse the sfr software. You could also use a piece of smooth matte inkjet paper for the backing; if you do that, you can print a Siemens star on it for focusing -- focusing on the slanted edge itself is difficult with an SLR (although easy with the Betterlight scanning back).  120 film would work, too. It's thinner, but it curls more. Developed film curls towards the emulsion side, which is the opposite of what you'd like.

Not developing the film is a possibility. That will reduce the contrast of the edge, but the film will lie flatter, and you probably don't need that much contrast anyway.

As A thinner alternative to photographic film, you might consider the black coated aluminum foil used in studio lighting, or industrial materials such as these:

http://www.tesa.com/industry/electronics/assortment_overview/functional_tapes/light_shading_blocking

The thinner the black material, the less chance of its casting a shadow, but the greater chance you'll bend and crinkle it trying to attach it. Try not to cut your own edge; the cutting equipment used by the material supplier will probably be smoother than anything you can do yourself.

If you have a white backing and a black edge maker, you're going to have a high-contrast target. Keep the exposure down far enough that the demosaicing and other processing doesn't cause clipping, or your sfr program will get confused.

Jim

Bart_van_der_Wolf

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Re: It's not binary
« Reply #91 on: October 27, 2014, 12:07:53 pm »

The thinner the black material, the less chance of its casting a shadow, but the greater chance you'll bend and crinkle it trying to attach it. Try not to cut your own edge; the cutting equipment used by the material supplier will probably be smoother than anything you can do yourself.

If you have a white backing and a black edge maker, you're going to have a high-contrast target. Keep the exposure down far enough that the demosaicing and other processing doesn't cause clipping, or your sfr program will get confused.

In the past I've used simple self adhesive black, and self adhesive white PVC material one can use to cover shelves. Using the black material at the bottom, and cut with a sharp knife the white on top, will make the black shine through a bit and reduce the extreme contrast somewhat. The material is also rather thin, and won't cast much of a shadow, which would fall on the black layer and be hardly invisible anyway. It's also weatherproof in case one needs to shoot a test outside and can't wait for better weather.

Cheers,
Bart
« Last Edit: October 27, 2014, 12:10:46 pm by BartvanderWolf »
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Re: Do Sensors “Outresolve” Lenses?
« Reply #92 on: October 28, 2014, 12:46:53 am »

How accurate would say this Blog is on understanding diffraction
https://dtmateojr.wordpress.com/2014/10/09/understanding-the-effects-of-diffraction/
And would you recommend the site for beginners  ?
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Bart_van_der_Wolf

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Re: Do Sensors “Outresolve” Lenses?
« Reply #93 on: October 28, 2014, 04:01:22 am »

And would you recommend the site for beginners  ?

His account on DPReview seems to have been terminated, and I remember some heated debate over there, with some other actually very well informed contributors. The blog doesn't seem worth the time to untangle the correct from the incorrect statements, especially for 'beginners'. Your mileage may vary.

Cheers,
Bart
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Re: It's not binary
« Reply #94 on: October 28, 2014, 06:27:05 pm »



 I had a renewed interest in this when I first seen this Lensrentals charts




When we take a look at the 50 1.8 G with 5.92 µm µm pixel D3x

to a 50mm 1.8 G 3.39 µm pixel V1






 I have been told countless times that the work presented by Lensrental and photozone are bogus on another sight and would welcome your insight as to why a higher resolution sensor would show a different Fstop at which the system (sensor and lens) peaks  
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ErikKaffehr

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Re: It's not binary
« Reply #95 on: October 28, 2014, 07:00:37 pm »

Hi,

Hard to explain that MTF 50 reaches max smaller apertures, but I would guess it may have to do with focusing. Latest generation Canon lenses and cameras have considerably better AF than older cameras. Exact focusing using LV may be easier on newer cameras.

Another point is that the peak is quite coarsely sampled. The lenses probably peak somewhere between f/5.6 and f/8.

A third observation is that the MTF fifty figure measures the frequency where MTF reaches 50%, so higher resolution cameras are measured at a different point of the MTF curve than lower resolution cameras. Would the plot show MTF at say 40 lp/mm the peaking may be different.

Something that needs to be pointed out is that Lensrentals measurements use DCRaw without sharpening while Photozone uses Lightroom with standard sharpening. The Lensrental values are presented as lp/picture height while Photozne data is LW/picture height, so the data differs by a factor of two, simply because of nomenclature.

Best regards
Erik




I have been told countless times that the work presented by Lensrental and photozone are bogus on another sight and would welcome your insight as to why a higher resolution sensor would show a different Fstop at which the system (sensor and lens) peaks  
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Ian stuart Forsyth

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Re: It's not binary
« Reply #96 on: October 29, 2014, 02:40:59 am »

I have been told countless times that the work presented by Lensrental and photozone are bogus on another sight and would welcome your insight as to why a higher resolution sensor would show a different Fstop at which the system (sensor and lens) peaks  
I believe what is happening is that we can more precisely detect the point where we see the meeting points of blur from  Aberrations and diffraction. With the D700 the blur from being resolution limited is hiding the point that blur from aberrations start to limit the contrast in the image. Kind of like using a meter stick with cm accuracy and then measuring a second time with a stick to the 1mm accuracy and finding that you have 2 different final measurements.

The problem at this point in time is we don’t know what the peak f-stop is of a lens, until we can accurately measure every photon strike the lens projects. It’s kind of like we don’t know the point that a  soft lens stops resolving detail not until we hit the limit of light. If we had a true MTF graph that showed the  resolution of a lens through different F stops what we would see is as the pixels get small and smaller the data collect would move closer and closer to that line.  This manifest itself in a  MTF graph as a smaller and smaller F-stop as the pixel size gets smaller its moving closer to that absolute line.  In other words the lens peaks the same but how we measure where the sensor peaks with that lens differs.  
« Last Edit: October 30, 2014, 12:30:50 am by Ian stuart Forsyth »
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