How much sensor resolution do we need to match our lenses?

[Jim Kasson]

Whether any f-stop except f/16 is diffraction-limited will take some more work, but diffraction is clearly adversely affecting f/11.

Here's a comparison of the actual Sony a7R/Otus 55/1.4 slanted edge MTF vs the results of my camera simulator modeling a camera of the same pixel pitch with a diffraction limited perfect lens at 550 nm illumination.



It looks like the Otus is diffraction-limited at f/11, and pretty close at f/8.

I'll do a complete write-up on this, but I've been programming all afternoon, and just want to get the results up now.

Jim

[Fine_Art]

Here's a comparison of the actual Sony a7R/Otus 55/1.4 slanted edge MTF vs the results of my camera simulator modeling a camera of the same pixel pitch with a diffraction limited perfect lens at 550 nm illumination.



It looks like the Otus is diffraction-limited at f/11, and pretty close at f/8.

I'll do a complete write-up on this, but I've been programming all afternoon, and just want to get the results up now.

Jim

I don't understand that. Are you saying resolution will not increase at apertures wider than f11?

[Jim Kasson]

I don't understand that. Are you saying resolution will not increase at apertures wider than f11?

No, the MTF plots show resolution increasing as the lens is opened  up all the way to f/5.6, but not as much as a diffraction-limited lens at apertures wider than f/11.

Jim

[Fine_Art]

My understanding of the term diffraction limited is the point at which diffraction reduces resolution. It would be the peak, first derivative = 0. Are you using a different (engineering) definition? The graph of the Otus looks wrong either way. I find it hard to believe it maxes out at f 5.6. I read a review that said f2.

[Fine_Art]

Cross posted. Ok, so you are saying the perfect lens, with only diffraction would be the higher curve, a real lens, with other components in the PSF is blending the aberations with diffraction.

[Jim Kasson]

My understanding of the term diffraction limited is the point at which diffraction reduces resolution. It would be the peak, first derivative = 0. Are you using a different (engineering) definition?

By diffraction-limited, I mean that the resolution is essentially determined by diffraction. All lens defects (other than diffraction, if you consider that to be a defect), are not material. The traditional way to say that is, "An optical system with the ability to produce images with angular resolution as good as the instrument's theoretical limit is said to be diffraction limited."

The graph of the Otus looks wrong either way. I find it hard to believe it maxes out at f 5.6. I read a review that said f2.

Please cite the review.

Thanks,

Jim

[Jim Kasson]

Cross posted. Ok, so you are saying the perfect lens, with only diffraction would be the higher curve, a real lens, with other components in the PSF is blending the aberations with diffraction.

That's what I'm saying, although I would not have said it quite that way.

Jim

[ErikKaffehr]

Hi,

I am pretty sure Otus maxes somewhere around f/4, see figure below from Lensrentals

DxO-mark shows similar data.

My understanding is that the classic definition is that on a diffraction limited lens the first Airy ring can be clearly seen.

Note that Lensrentals uses LP/IH and not the more usual LW/IH, which gives half the figure and also that they don't use sharpening.

Best regards
Erik

By diffraction-limited, I mean that the resolution is essentially determined by diffraction. All lens defects (other than diffraction, if you consider that to be a defect), are not material. The traditional way to say that is, "An optical system with the ability to produce images with angular resolution as good as the instrument's theoretical limit is said to be diffraction limited."

Please cite the review.

Thanks,

Jim

[Jim Kasson]

I am pretty sure Otus maxes somewhere around f/4, see figure below from Lensrentals. DxO-mark shows similar data.

Erik, the LR curve shows on-axis performance of the Otus at f/4 slightly better than f/5.6. My testing shows it slightly worse. The difference is not large, and could be due to:

statistical variation (there are no confidence lines or bars on the LR curves)
difference contrast targets (I used a contrast of 4, in Imatest terms)
difference lighting spectra (I used a studio strobe)
sample variations in the lens
not using the same shutter speed for all tests (I varied the light level. If someone didn't do that, but compensated for exposure as the f-stop is opened up by increasing shutter speed, that could reduce vibration on the widers aperture test images
a different sensor (I'm assuming that the LR test images were made with a D800E, although you didn't say so. The D800E has a strange "non-AA" filter. I believe the a7R has none)
many other things

I don't consider the differences in the two test results to be particularly important.

My understanding is that the classic definition is that on a diffraction limited lens the first Airy ring [you mean the zero, I believe] can be clearly seen.

I don't have an optical bench. If I did, that's the test I would have performed; it's the gold standard. A 36 MP sensor can't clearly resolve the Airy pattern even af f/16. SO I used a more indirect way to get the answer. I thought it was pretty clever, but I've always been a big fan of my own ideas.

Note that Lensrentals uses LP/IH and not the more usual LW/IH, which gives half the figure and also that they don't use sharpening.

We both use Imatest. I didn't use sharpening either. I took the readouts in cycles/pixel, and converted them to cycles/picture height for the full frame. As has been discussed in this thread, a line pair is a cycle, and line pairs/PH should be close to (exactly?) cycles/PH.  

But the LR numbers are way too low for a 36 MP sensor, which is 4912 pixels high and can theoretically resolve half that many line pairs. I think I know what happened. Imatest reports results in LW/PH based on the height of the sample image it sees. I always feed it a cropped image, and thus any readout that is per picture height is looking at the wrong height. It's possible that the LR folks didn't correct for that, figuring, quite properly, that the absolute numbers weren't important, just the relative ones.

Eric, have you seen any claims that the Otus is the sharpest at f/2?

Jim

[ErikKaffehr]

Jim,

I guess I responded to the wrong posting…. My response was more direct to "FineArt"

Anyway, from what I have seen the Otus peaks somewhere between f/4 and f/5.6.

The Lensrentals data is interesting, but the data they present is much lower than the data normally reported. I guess they use DC-raw for conversion. I felt it needed to be pointed out that they use LP (line pairs) and not LW (line widths) which may be more common.

I think there is some variation in Imatest results depending on target and other factors. My guess is that demosaic technique also plays a role. In one case I have seen that LR and Capture one was very close but RawTherapee gave different Imatest results. I also found that another experienced and knowledgeable poster got slightly better results with ACR than what I got in Lightroom on the same image. Maybe the are improvements in ACR that are still not in LR 5.4?

I am thankful you started this thread and also for sharing the findings of your research.

Best regards
Erik

Eric, the LR curve show on-axis performance of the Otus at f/4 slightly better than f/5.6. My testing shows it slightly worse. The difference is not large, and could be due to:

statistical variation (there are no confidence lines or bars on the LR curves)
difference contrast targets (I used a contrast of 4, in Imatest terms)
difference lighting spectra (I used a studio strobe)
sample variations in the lens
not using the same shutter speed for all tests (I varied the light level. If someone didn't do that, but compensated for exposure as the f-stop is opened up by increasing shutter speed, that could reduce vibration on the widers aperture test images
a different sensor (I'm assuming that the LR test images were made with a D800E, although you didn't say so. The D800E has a strange "non-AA" filter. I believe the a7R has none)
many other things

I don't consider the differences in the two test results to be particularly important.

I don't have an optical bench. If I did, that's the test I would have performed; it's the gold standard. A 36 MP sensor can't clearly resolve the Airy pattern even af f/16. SO I used a more indirect way to get the answer. I thought it was pretty clever, but I've always been a big fan of my own ideas.

We both use Imatest. I didn't use sharpening either. I took the readouts in cycles/pixel, and converted them to cycles/picture height for the full frame. As has been discussed in this thread, a line pair is a cycle, and line pairs/PH should be close to (exactly?) cycles/PH.  

But the LR numbers are way too low for a 36 MP sensor, which is 4912 pixels high and can theoretically resolve half that many line pairs. I think I know what happened. Imatest reports results in LW/PH based on the height of the sample image it sees. I always feed it a cropped image, and thus any readout that is per picture height is looking at the wrong height. It's possible that the LR folks didn't correct for that, figuring, quite properly, that the absolute numbers weren't important, just the relative ones.

Eric, have you seen any claims that the Otus is the sharpest at f/2?

Jim

[Jim Kasson]

The Lensrentals data is interesting, but the data they present is much lower than the data normally reported. I guess they use DC-raw for conversion. I felt it needed to be pointed out that they use LP (line pairs) and not LW (line widths) which may be more common.

I think there is some variation in Imatest results depending on target and other factors. My guess is that demosaic technique also plays a role. In one case I have seen that LR and Capture one was very close but RawTherapee gave different Imatest results. I also found that another experienced and knowledgeable poster got slightly better results with ACR than what I got in Lightroom on the same image. Maybe the are improvements in ACR that are still not in LR 5.4?

Erik, you are absolutely right that the slanted edge MTF results are sensitive to the demosaicing algorithm. Even naming the demosacing program doesn't completely specify the algorithm -- DCRAW offers four algorithms, from bilinear interpolation to adaptive homogeneity-directed interpolation. Some of these algorithms seem to do sharpening, which makes the absolute MTF get larger.

We should remember that the absolute MTF numbers are not the important thing in a f-stop series like this -- there are too many variables that affect them. The relative numbers seem to hold up over a range of demosaicing techniques, for which I am grateful.

Jim

[Fine_Art]

I did a brief search for the review, could not spot it on the first 2 pages of returns.

Erik's f4 is more likely. I will go with that.

This review has a higher figure
"I used Imatest to check the sharpness of the Otus using a standard SFRPlus test chart. At f/1.4 it’s an outstanding performer, scoring 3,015 lines per picture height on a center-weighted test. That’s much, much higher than the 1,800 lines we require for a photo to be called sharp, and impressively the extreme edges of the frame are just as sharp as the center. It only gets better as you stop down: 3,265 lines at f/2, 3,602 lines at f/2.8, 3,829 lines at f/4, 3,899 lines at f/5.6, and 3,951 lines at f/8. Distortion is a nonissue; the lens shows 0.7 percent barrel distortion, but that’s barely relevant in field conditions. There’s no evidence of falloff at the corners; the vignette in the shot below was added in Lightroom.
Read more at http://www.itreviews.com/zeiss-otus-1-455/#LScdCVIPGVimjE26.99"

It does not really matter in the real world, we will not give up DoF for a few more lines of resolution.

[ErikKaffehr]

Hi,

Just as a small point, the reason the Otus is that expensive is that it pushes performance at large apertures. Most decent lenses are pretty sharp at medium apertures.

I include some MTF data from DxO mark, comparing Nikon 50/1.8, Sigma 50/1.4 EX (not the A-series) and Zeiss Otus

The Zeiss really shines at maximum aperture, but stopping down to f/2.8 removes much of the advantage. At f/8 there is not much between the lenses.

It may be argued, that buying an Otus for shooting medium apertures makes little sense. In addition, the Otus has an awful lot of glass which may make it more sensitive to flare and ghosting.

I would make a point for making well corrected medium aperture lenses like f/2.8.

Regarding MTF data, it needs to be considered what is mesaured and how it is presented.

For instance, for lens testing I normally use Lightroom 5.4 with no sharpening, Photozone uses default sharpening, some may use out of camera JPEGs and some may even use two stage sharpening.

For SQF evaluation I normally use Landscape sharpening in Lightroom 5.3.

Best regards
Erik

I did a brief search for the review, could not spot it on the first 2 pages of returns.

Erik's f4 is more likely. I will go with that.

This review has a higher figure
"I used Imatest to check the sharpness of the Otus using a standard SFRPlus test chart. At f/1.4 it’s an outstanding performer, scoring 3,015 lines per picture height on a center-weighted test. That’s much, much higher than the 1,800 lines we require for a photo to be called sharp, and impressively the extreme edges of the frame are just as sharp as the center. It only gets better as you stop down: 3,265 lines at f/2, 3,602 lines at f/2.8, 3,829 lines at f/4, 3,899 lines at f/5.6, and 3,951 lines at f/8. Distortion is a nonissue; the lens shows 0.7 percent barrel distortion, but that’s barely relevant in field conditions. There’s no evidence of falloff at the corners; the vignette in the shot below was added in Lightroom.
Read more at http://www.itreviews.com/zeiss-otus-1-455/#LScdCVIPGVimjE26.99"

It does not really matter in the real world, we will not give up DoF for a few more lines of resolution.

[Jim Kasson]

I include some MTF data from DxO mark, comparing Nikon 50/1.8, Sigma 50/1.4 EX (not the A-series) and Zeiss Otus

Erik, it looks to me like the Otus tests were made on a D800 with its AA filter, and the other two lenses ere tested on a D800E with no (well, OK, a now-you-see-it-now-you-don't) AA filter.

Jim

[Jim Kasson]

It may be argued, that buying an Otus for shooting medium apertures makes little sense.

Erik, that's not the way it appears to me. I find the contrast and drawing amazing even at f/11. If I were you, I'd not pay much attention to that, since I'm not backing it up with numbers. However, you might want to read what a real expert has to say on the subject.

http://www.luminous-landscape.com/forum/index.php?topic=89877.0

Jim

[Manoli]

Jim,

I know you've compared the LEICA 50 ‘LUX ON THE M240 v SONY 55 FE ON THE SONY A7, but out of interest have you compared the Leica 50'LUX against the Zeiss Otus ?

Manoli

[Jim Kasson]

I know you've compared the LEICA 50 ‘LUX ON THE M240 v SONY 55 FE ON THE SONY A7, but out of interest have you compared the Leica 50'LUX against the Zeiss Otus ?

The 50 'lux on the a7R suffers from corner smearing, so I lost interest in testing it on that camera. I can't use the Leica lens on the D800E. I suppose I could test both on the M240, but it would take me half a day, and would anybody really use the Otus on the M240?

Jim

[Manoli]

I suppose I could test both on the M240, but it would take me half a day, and would anybody really use the Otus on the M240?

No, you're right although when I (very) briefly tested the 50 on the a7r I didn't find any noticeable corner smearing, unlike many of the wide-angles which are, IMO, next to unusable, unfortunately. I've a strange hunch though that Leica may well produce an M-EVF competitor to the a7 series by Photokina.  We'll see ..

All Best,
Manoli

ps
Thanks for the link.

[ErikKaffehr]

Hi,

Thanks for info. For me it is a bit surprising, but I have no Otus, so it is not personal experience. Thanks for pointing out the issue with D800/D800E, I missed it entirely.

Have you any idea why Otus would be less affected by diffraction than other lenses? Of course, it has a better starting point. The other question may be how far a simpler lens may be from the diffraction limit at medium aperture.

Best regards
Erik

Erik, that's not the way it appears to me. I find the contrast and drawing amazing even at f/11. If I were you, I'd not pay much attention to that, since I'm not backing it up with numbers. However, you might want to read what a real expert has to say on the subject.

http://www.luminous-landscape.com/forum/index.php?topic=89877.0

Jim

[Bart_van_der_Wolf]

Hi,

Thanks for info. For me it is a bit surprising, but I have no Otus, so it is not personal experience. Thanks for pointing out the issue with D800/D800E, I missed it entirely.

Have you any idea why Otus would be less affected by diffraction than other lenses? Of course, it has a better starting point. The other question may be how far a simpler lens may be from the diffraction limit at medium aperture.

Hi Erik,

It's not that the Otus somehow has less diffraction, it just suffers less. One needs to understand that diffraction is one of several sources of blur, residual lens aberrations being another lens related source. These blurs add, the MTFs after convolution with the PSF of diffraction, and the PSF of aberrations, multiply. That means that the lesser of the two MTFs dictates the resulting lens MTF.

It is not just that, but the system MTF also depends on the sensel aperture and sampling density, and there may be an OLPF involved as well. All these (there is also an IR filter and sensor cover-glass) have an individual MTF that leads to a total combined MTF. So the lens MTF will be modified by the rest of the system.

All-in-all, the better the lens, the better the total performance will be, and the Otus does not leave much to be desired in that equation. That quality will also survive to a large extent to the OOF regions, so it may look a bit more pleasing, and may be easier to restore with deconvolution sharpening, QED ...

Cheers,
Bart