How much ff resolution to not be "weak link" with Otus?

[l_d_allan]

My understanding is that the very expensive Zeiss 55mm f1.4 Otus is pretty much state-of-the-art for lens quality, including line-pair resolution.

I also have the impression that the Otus has more resolution than even the Nikon D800e with 36mpx can resolve. In that sense, the Nikon sensor is the "weak link".

• I'm unclear if this is a valid question, but what full frame sensor resolution would "balance" the Otus so that neither was the "weak link"?
• How about APS-C sensors with 24 mpx and no AA filter? I believe I've read that these sensors present the greatest challenge to the center of premium lenses.
• Is there some kind of formula that relates optimal sensor resolution to line-pair resolution with a certain MFT definition?
• How about very good, but not ultra-premium lenses like a Canon 35mm f2 IS prime?
• How about a very good zoom like the Canon 70-200mm f2.8L II zoom?
• Is there a way to estimate how much resolution a lens can "feed" from DxoMark lens ratings?
• Sorry if this question has been asked before.

 

[Mark S Abeln]

• Is there a way to estimate how much resolution a lens can "feed" from DxoMark lens ratings?

We can see this on DxOMark when we examine the P-Mpix or Sharpness value for a lens. Typically, as you compare this value for any given lens with as megapixels go up and as antialias filters get weaker or are removed, eventually it will stagnate — that is, it won’t delver any better P-Mpix values for better-resolving bodies — the lens has reached its limit. There appear to be some lenses which haven’t reached their limit yet, as they show improvement continuously until they hit the D800E wall.

What is rather more difficult is to determine the practical upper limit for camera bodies. There are two factors to consider, including the softening effect of the antialias filter — there is a lot of variation — and also the fact that most lenses tend to be sharper in the center.

You will often see a particularly body that can’t delver more than a certain amount of P-Mpix with a wide variety of lenses, and then you see one lens which exceeds the rest — this is often due to a lens with a nice flat field and corner-to-corner sharpness. With other lenses, the center sharpness hits the wall of maximum resolution on a camera, while the corners are under-resolved. However, it is possible that a particular lens, with lots of contrast, may “overpower” (whatever that means) the antialias filter more than its peers — don’t quote me on this — but I think that can be seen in the data. An interesting example of this is the D7000, which seemed to have an upper of 11 P-Mpix for a good number of the best quality lenses, until the new expensive Carl Zeiss lenses came out — then we unexpectedly see that it can deliver at least 14 P-Mpix.

Just looking at the data, I think there is good evidence of the old camera rule-of-thumb of ‘glass over body’ — especially as we have lots of cameras with plenty of megapixels, as well as plenty of poorly-performing lenses.

Also, be aware that really fine full-frame lenses won’t perform quite as well as expected on a crop sensor camera, since the latter bodies are cramming more pixels into a smaller area.

--

The Refracted Light

A website about the Art and Science of Photography

therefractedlight.blogspot.com

 

[Roland Karlsson]

Also, be aware that really fine full-frame lenses won’t perform quite as well as expected on a crop sensor camera, since the latter bodies are cramming more pixels into a smaller area.

Eh?

Cramming more pixel per area is exactly what is needed if the lens is sharp.

 

[Roland Karlsson]

My understanding is that the very expensive Zeiss 55mm f1.4 Otus is pretty much state-of-the-art for lens quality, including line-pair resolution.

I also have the impression that the Otus has more resolution than even the Nikon D800e with 36mpx can resolve. In that sense, the Nikon sensor is the "weak link".

It does not really matter what very good lens you take. They all have the same order of resolution at max resolution. i.e. while stopped down some.

http://www.lenstip.com/390.4-Lens_review-Carl_Zeiss_Otus_55_mm_f_1.4_ZE_ZF.2_Image_resolution.html

As you can see, otus is fantastic - at full opening. But at max resolution you have 45-50 lp/mm for all lenses. Yeah, the difference matters some, but it is in the same order.

So, what is needed to sample 50 lp/mm?

In some kind of simplified view you need 10 um pixels, and a 36 MP FF has 5 um pixels. But, this is obviously not true. Anyone?

 

[xpatUSA]

At f/1.4 the perfect lens falls to zero MTF at 1287 lp/mm.

cf. lumolabs.com

At 50 lp/mm the lens MTF is 95%.

web.ncf.ca/jim/misc/resolution/mtf/

At 50 lp/mm and 10um pixel pitch the sensor is exactly at Nyquist with an MTF of 41%.

Sensor MTF = sinc^2(pi x lp/mm/(px/mm))

Combining these two MTFs, we get 38%.

 

[Mark S Abeln]

Also, be aware that really fine full-frame lenses won’t perform quite as well as expected on a crop sensor camera, since the latter bodies are cramming more pixels into a smaller area.

Eh?

Cramming more pixel per area is exactly what is needed if the lens is sharp.

You are right. That was poorly worded.

A really fine lens, like the new Otus, performs exceptionally well on a crop-sensor D7100 — compared to the D800, 21 versus 29 P-Mpix, because the lens probably hasn’t reached its camera megapixel limit.

For inferior lenses, you are cropping out more of the potential detail deliverable by the lens, since they are at their megapixel limit already.

--

The Refracted Light

A website about the Art and Science of Photography

therefractedlight.blogspot.com

 

[Roland Karlsson]

At f/1.4 the perfect lens falls to zero MTF at 1287 lp/mm.

cf. lumolabs.com

At 50 lp/mm the lens MTF is 95%.

web.ncf.ca/jim/misc/resolution/mtf/

At 50 lp/mm and 10um pixel pitch the sensor is exactly at Nyquist with an MTF of 41%.

Sensor MTF = sinc^2(pi x lp/mm/(px/mm))

Combining these two MTFs, we get 38%.

Nice, but I assume the real question is - what pixel pitch is needed not to degrade the 50 lp/mm (too much).

 

[xpatUSA]

Nice, but I assume the real question is - what pixel pitch is needed not to degrade the 50 lp/mm (too much).

OK, at what MTF would the 50 lp/mm be not degraded 'too much'? Would that be the oft-stated 50%, perhaps?

If so, I make it 8.5um.

--
Cheers,
Ted

 

[J C Brown]

At f/1.4 the perfect lens falls to zero MTF at 1287 lp/mm.

cf. lumolabs.com

At 50 lp/mm the lens MTF is 95%.

web.ncf.ca/jim/misc/resolution/mtf/

At 50 lp/mm and 10um pixel pitch the sensor is exactly at Nyquist with an MTF of 41%.

Sensor MTF = sinc^2(pi x lp/mm/(px/mm))

Combining these two MTFs, we get 38%.

Nice, but I assume the real question is - what pixel pitch is needed not to degrade the 50 lp/mm (too much).

 

[Roland Karlsson]

Thank you both.

Then current sensors are enough for OTIS.

 

[Roland Karlsson]

Thank you both.

Then current sensors are enough for OTIS.

Actually, this is a surprise to me.

One thought, have we now considered the Nyquist criteria - that you need to sample with twice the frequency than the highest frequency in the signal?

Shall we not double the sensor resolution? To begin with?

And do we really catch all what the lens can provide?

 

[John Sheehy]

My understanding is that the very expensive Zeiss 55mm f1.4 Otus is pretty much state-of-the-art for lens quality, including line-pair resolution.

I also have the impression that the Otus has more resolution than even the Nikon D800e with 36mpx can resolve. In that sense, the Nikon sensor is the "weak link".

The sensor has discrete resolution, and the lens has analog resolution, as different as apples and oranges. No sensor fully resolves any lens. Both work towards limiting resolution. There is no thresholding involved.

• I'm unclear if this is a valid question, but what full frame sensor resolution would "balance" the Otus so that neither was the "weak link"?

I would guess that at about 500 MP FF or so, the best lenses have very little more to give.

• How about APS-C sensors with 24 mpx and no AA filter? I believe I've read that these sensors present the greatest challenge to the center of premium lenses.

Nikon D7100s are aliasing with consumer-grade lenses.

• Is there some kind of formula that relates optimal sensor resolution to line-pair resolution with a certain MFT definition?

To capture a line pair with luck of alignment, no AA filter and one pixel row or column per line will work. As soon as it gets out of phase or alignment, though, the line pairs will distort and break up. This is horrible imaging (not the same as "bad photography", of course, as many interesting photos are technically broken). A more reasonable common standard is about 1.4 camera lines per lens line, but that is not ideal, IMO, and I would take it further, and say that a B&W or Foveon sensor needs about 3 sensor lines per lens line to be distortion-free, and a Bayer sensor, 6 lines. That of course, is very expensive by today's standards in terms of needed storage and CPU power for processing. It comes very close to practicality, however, for someone doing something like heavily cropping small subjects with a DSLR; a compact sensor attached to a DSLR lens gives much better results. If I attach my Pentax Q to my DSLR telephoto and shoot a detailed object, and shoot with my DSLRs from the same distance with the same lens, the latter looks like cr@p compared to the former, unless the DSLR is my 6D and the ISO is 3200 or above, because the 6D has state-of-the art low high-ISO noise. The 7D and my older 5DmkII can't touch the Q, even at high ISOs.

• How about very good, but not ultra-premium lenses like a Canon 35mm f2 IS prime?
• How about a very good zoom like the Canon 70-200mm f2.8L II zoom?

I've seen 100% crops from this lens with a 2x and 1.4x TC stacked on a 7D that had pixel-level detail visible with mild sharpening. That's with a strong AA filter on the 7D. The same or better would be possible without the TC, and 8x the pixel density, or about 143 MP, APS-C 1.6x; especially with no AA filter.

• Is there a way to estimate how much resolution a lens can "feed" from DxoMark lens ratings?

The closer the "perceptual MP" is to the actual MP of the sensor used, the much further beyond the MP of the sensor that could be easily appreciated with high returns. Of course, a strong AA filter lowers the "PMP" from what it would be without one or with a weaker one.

The bottom line is that all current MP counts are insufficient for all half-way decent lenses, especially in their sweet spots. We are taking shortcuts that distort the analog image projected by the lens with AA filters and/or low pixel densities. Keeping MP counts low to keep pixel-level (100% pixel view) sharpness high is counter-productive to imaging, and only helps with processing speed and storage space issues. The best capture is one where there is so much pixel density that everything is soft at the pixel level on a ~100 PPI monitor, except the noise, which can be much more effectively identified and eliminated. The resulting capture is immune to damage such as sharpening halos, loss of detail from CA and geometric corrections, rotation, scaling, etc. An image capture sharp at the pixel level can be interesting eye candy, but is a fragile mess of partial and distorted sharpness that breaks down as soon as you try to do any editing to it.

 

[John Sheehy]

Nice, but I assume the real question is - what pixel pitch is needed not to degrade the 50 lp/mm (too much).

Define "degrade". Any capture that has significant contrast between neighboring pixels is degraded by too little pixel density, IMO, and that includes the red and blue sub-images of a CFA capture.

 

[John Sheehy]

Thank you both.

Then current sensors are enough for OTIS.

Hardly. I bet the OTUS aliases on a Pentax Q, at least in the blue channel.

 

[John Sheehy]

And do we really catch all what the lens can provide?

Not at all. The lens can provide an analog projection, which has no dependence on luck of subject/pixel alignment, and can be corrected for geometric distortions with no loss of detail, real or artificial (as what you get in an aliasing capture when you have to move pixel transients to the middle of pixels and lose your "3D pop").

 

[xpatUSA]

Thank you both.

Then current sensors are enough for OTIS.

Hardly. I bet the OTUS aliases on a Pentax Q, at least in the blue channel.

Got my interest there, John, with that one-liner. What is the pixel pitch of that camera and at what spatial frequency would the aliasing commence?

Thanks,

 

[Roland Karlsson]

John Sheehy wrote:
Define "degrade". Any capture that has significant contrast between neighboring pixels is degraded by too little pixel density, IMO, and that includes the red and blue sub-images of a CFA capture.

Yepp, it is a Bayer CFA after all.

There are three possibilities:

1. There exist a sampling Bayer CFA grid where increasing the sampling frequency will not (theoretically) give us more information about the image from the OTIS lens.
2. There exist a sampling Bayer CFA grid where increasing the sampling frequency will not (in practice) matter for the usage of the camera, when using the OTIS lens.
3. Both 2 and 1 are false.

And ... if any of 1 or 2 is true, then it is possible to give a pixel pitch that is the limit.

So .... my question is, what may this limit be?

Is 1 um enough?

 

[J C Brown]

Thank you both.

Then current sensors are enough for OTIS.

Actually, this is a surprise to me.

One thought, have we now considered the Nyquist criteria - that you need to sample with twice the frequency than the highest frequency in the signal?

Shall we not double the sensor resolution? To begin with?

And do we really catch all what the lens can provide?

 

[Mark S Abeln]

• How about APS-C sensors with 24 mpx and no AA filter? I believe I've read that these sensors present the greatest challenge to the center of premium lenses.

Nikon D7100s are aliasing with consumer-grade lenses.

But could some of that aliasing be from the demosaicing algorithm? Especially since this doesn’t have an AA filter?

 

[Jack Hogan]

Is 1 um enough?

Unless we figure something else out it better be, since it appears that it is not easy to go below that once we take physics into account (accuracy of focusing, diffraction, microlenses etc.)