Speculations on the megapixel race or "Do I need a + 32 Megapixel sensor?"

[Chewy734]

tjshot, thanks for the writeup... I appreciate the time you took to write that article.

 

[tjshot]

tjshot, thanks for the writeup... I appreciate the time you took to write that article.

Not at all!
It really was written out of personal curiosity.

 

[GeorgeMaciver]

Thanks for that article by Ken Rockwell, Candyman, I'm planning lowering the resolution of my RAWs next time I'm out, to test out what he says.

8)

 

[torger]

On the print side, doesn't anyone do c-prints any longer? I find it quite nice to order large prints from the lab. I usually do a couple of smaller test prints to verify color, brightness etc and then order the final size for fine art framing. Unlike ordering inkjet prints, c-print results are very predictable, those machines are kind of fool-proof. The main drawback is that you really only can get a single glossy photo look, there is not the wide choice of papers as for inkjets. But if you like glossy c-print is one of the best.

What I'm saying is that you don't need to be a pro to do prints larger than 13x19. To me it is more common that I do prints which is larger than this format than the other way around.

Another thing is that in 30 years I may want to make prints of pictures I made this year. I don't know what print technology will exist then. So I don't really like to limit the camera sensor to commonly available print technology if you don't need to.

 

[tjshot]

What I'm saying is that you don't need to be a pro to do prints larger than 13x19. To me it is more common that I do prints which is larger than this format than the other way around.

Another thing is that in 30 years I may want to make prints of pictures I made this year. I don't know what print technology will exist then. So I don't really like to limit the camera sensor to commonly available print technology if you don't need to.

For me it's more a matter of optimizing investment to actual requirements: I'd rather put my money on an pro lens that will stay with me for years, than on a (relatively) short-lived camera body.
So I just choose the camera accordingly.
Moreover I see 13x19 inches from a single shot as the perfect top size for quality personal prints: archive size is still manageable and they are big enough to appreciate fine details.
If I'll ever need to print the same image larger I could still interpolate with decent results or do digital mosaics; with a bit of knowledge even a cheap pano setup can give excellent results.
Thats why I look forward to a 32 Mpxls body, as it perfectly fits my needs.
Every further increase in res. should be evaluated against noise and dynamic range performance.

 

[torger]

Thats why I look forward to a 32 Mpxls body, as it perfectly fits my needs.
Every further increase in res. should be evaluated against noise and dynamic range performance.

I shall say that also agree that 32 megapixels would be an excellent resolution for 5Dmk3, especially without AA filter. Above 30 it will be much about lens resolving power anyway. High contrast pixels at 32 megapixels (thanks to a sharp lens and no AA filter) could give a sharper image in print than low contrast at 45...

Already today the APS-C cameras 18 megapixels is kind of out-resolving lenses, the individual pixels are not particularly high contrast. You may be getting almost the same resolution from a 12 megapixel fullframe camera as from an 18 megapixel APS-C, depending on lens.

I don't see it as a big disadvantage to out-resolve lenses though, with bayer array it can be nice to out-resolve a little, and if you need to rotate or perspective adjust the image it can be nice to have "soft" pixels since you will not reduce image quality as much as if the pixels are supersharp. Deconvolution can also restore a bit of the resolution. However, if there is DR and noise gains to have larger pixels that will be more valuable before starting to outresolve lenses.

32 seems like a good number today, because then you both increase the resolution significantly but still have larger pixels than on the modern APS-C sensors.

 

[tjshot]

Thats why I look forward to a 32 Mpxls body, as it perfectly fits my needs.
Every further increase in res. should be evaluated against noise and dynamic range performance.

I shall say that also agree that 32 megapixels would be an excellent resolution for 5Dmk3, especially without AA filter. Above 30 it will be much about lens resolving power anyway. High contrast pixels at 32 megapixels (thanks to a sharp lens and no AA filter) could give a sharper image in print than low contrast at 45...

Already today the APS-C cameras 18 megapixels is kind of out-resolving lenses, the individual pixels are not particularly high contrast. You may be getting almost the same resolution from a 12 megapixel fullframe camera as from an 18 megapixel APS-C, depending on lens.

I don't see it as a big disadvantage to out-resolve lenses though, with bayer array it can be nice to out-resolve a little, and if you need to rotate or perspective adjust the image it can be nice to have "soft" pixels since you will not reduce image quality as much as if the pixels are supersharp. Deconvolution can also restore a bit of the resolution. However, if there is DR and noise gains to have larger pixels that will be more valuable before starting to outresolve lenses.

32 seems like a good number today, because then you both increase the resolution significantly but still have larger pixels than on the modern APS-C sensors.

The concept of a sensor "outresolving" a lense is prone to many caveats.
Borrowing some infos from the document attached to original post, one could assume that to capture information from a real, excellent lense up to the MTF 10% (relevant resolution) a sensor would need to resolve:

about 90 lpm at F 16
about 135 lpm at F 11
about 159 lpm at F 8
about 195 lpm at F 5.6

Even a 50 Mpxls full frame sensor, or an equivalent-pitch 18 Mpxls APS-C one (EOS 7D), with proper sharpening applied, would be limited to about 115 lpm at MTF 10%: it would fall short of 20 lpm to reach the 135 lpm provided by the lense at F11.
For F 8 and F 5.6 the limit is even higher and would require an extremely dense sensor pitch, unpractical for actual CMOS technology due to poor noise and dynamic range performance.
Even a lense of average quality, in the F 4 to F 11 range, would probably be delivering "more information" than a 50 Mpxls sensor can actually resolve.

But the main thing to keep in mind is that limiting resolution, or Nyquist limit for a digital sensor, is not the only element to consider when evaluating performance.
A denser pixel pitch, after proper sharpening, can squeeze more information out of the same lense than a larger pitch one, even when the lense is performing below the Nyquist limit of both sensors (for example stopped down to F16 or smaller).
In other words the same lense stopped down to F16 would deliver better sharpness and resolution on a 50 Mpxls sensor than on a 36 or 21 Mpxls one, after proper sharpening is applied.
This is mainly due to the fact that a denser pitch generally allows to push sharpening further, for a similar SNR (Signal to Noise) ratio; moreover the higher Nyquist limit will allow to recover and sharpen even the high frequency information that a lower Nyquist limit would cut off.
Thus on a 50 Mpxls sensor you can squeeze 115 lpm @ MTF 10% out of an excellent lense stopped down to F16.
The main constraint is keeping up the SNR for smaller photosites so that they can produce a clean image and consequent better sharpening; up to this day it's been possible, mainly upgrading A/D converters to higher bit depth units, using better microlenses and optimizing the electronics.

So the whole imaging chain, i.e. lense + sensor, should be considered when evaluating performance: considering the lense only, then assuming a sensor would be "outresolving" it due to its higher Nyquist limit, is simply uncorrect.

For actual CMOS technology I believe a 32 Mpxls full frame sensor to be the optimal compromise and 50 Mpxls full frame sensor to be the practical limit ( if ever fast and effective 16 bit A/D converters can be introduced).

 

[torger]

The concept of a sensor "outresolving" a lense is prone to many caveats.
Borrowing some infos from the document attached to original post, one could assume that to capture information from a real, excellent lense up to the MTF 10% (relevant resolution) a sensor would need to resolve:

Yes "outresolving" is a simplified way to see it. Lens resolution is not a gating limit, even if you improve a factor in the chain that is not the largest "blur factor" the resolution will improve. However, you start to see diminishing returns when increasing sensor resolution over some limit, and how far you think it is meaningful to go is a matter of taste. With 18 megapixels on APS-C I think the point of diminishing returns has been passed, so I don't see it meaningful to increase it further.

My guess is that it is not meaningful to have such high resolution on the sensor that you can resolve down to MTF10% of the best part (center) of the best lenses. If combined with some clever deconvolution sharpening it perhaps can be, but unprocessed no.

It would be interesting to make a practical test with state of the art sharpening techniques and prints etc to find out how high resolution you need from a sensor relative your lens. I think the result would be that you need considerably less sensor resolution than the theoretical max.

 

[Edwin Herdman]

I'm trying to work through the attached PDF article, but the sans serif Courier New font makes it unreadable. Next time please use a serif font, for the love of my eyes.

 

[tjshot]

I'm trying to work through the attached PDF article, but the sans serif Courier New font makes it unreadable. Next time please use a serif font, for the love of my eyes.

Sorry!
I'll keep it in mind for the follow up I'll be posting in a few days, about sensor performance for a given print dpi and size.

 

[AprilForever]

I like megapixels. The more the merrier! But, I have reasons for liking them... Usually, my subject of choice, birds in flight, don't fill the frame, and often don't even come close to filling it...

The more the merrier! And hand me that stack of hard drives...

 

[tjshot]

Usually, my subject of choice, birds in flight, don't fill the frame, and often don't even come close to filling it...

That's the only situation in which a smaller sensor may perform better than a full frame one.
The same focal lenght will produce a "closer crop" with an higher pixel pitch.
Depending on the crop factor and pixel pitch density it can translate in better resolution and sharpness in final image.
For a given print size, the same F-stop will deliver a smaller DoF on crop sensor than on full frame, with worse SNR and Tone Separation for same ISO setting; however the higher sampling capability can eventualy make up for this cons.

If you often find yourself short of reach even with your most powerful tele, than a denser, smaller sensor is definitely the best choice.

 

[Edwin Herdman]

That is actually a more common scenario than just bird photography: Your best light prime lens can frame a speaker more tightly from the back of the room, or your fastest affordable f/1.4 lens (the 50mm) covers the very popular 80mm focal length range.

So it's not just reach - it's also price and weight, and possibly has other advantages as well (for example, try shooting a high resolution image on full frame with a 135mm tilt-shift lens - APS-C gets you much closer to this reality unless you're happy with the aperture and quality loss of coupling a 1.4X EF extender - and the 2X does nothing great for the TS-E 90mm).

 

[tjshot]

So it's not just reach - it's also price and weight, and possibly has other advantages as well (for example, try shooting a high resolution image on full frame with a 135mm tilt-shift lens - APS-C gets you much closer to this reality unless you're happy with the aperture and quality loss of coupling a 1.4X EF extender - and the 2X does nothing great for the TS-E 90mm).

I agree. There are situations where reduced FoV from crop sensors comes in handy.
However excellent prime lenses are required to really exploit the denser sensor pitch.

When it comes to tilt/shift lenses, for me DoF is the real constraint: I mainly use tilt to extend DoF for landscape shots, while I don't really feel the need to use it to isolate focus as long focal lenses do a good job wide open.
Enlarging to the same print size (A3 or more), full frame barely delivers enough DoF for a sharp down-tilt landscape shot, and that is for 24mm focal lenght or shorter (17mm). Even a 50mm is unusable in this scenario.
APS-C sensors simply don't provide enought depth to cover a large print.
That's the main reason why I still stick to using some film large format: there is no option in digital if you need a lot of DoF from a longer (equivalent) focal lense.

 

[Edwin Herdman]

Tilting the plane of deep focus is certainly more restricted on an APS-C camera than on a FF camera, but again this is a necessary evil for some applications because APS-C gives you (currently, and for the foreseeable future) the densest resolution for the longer framing. I mention TS-E lenses (and the same applies to macro lenses) not because the shift or tilt changes the rationale, but because there simply isn't any degree of tilt or shift available on lenses in focal length lenses longer than 90mm (unless you go to the very expensive Hartblei Superrotator 120 f/4 Makro lens).

While I haven't been able to do much for the near-macro capabilities of the TS-E 90mm on APS-C while also using tilt and shift (the effects of tilt especially are less pronounced close up, in seemingly the same way that the DOF slice is wider the further from the sensor plane you get), it's nice to have any control at all.

Also don't agree that you need a great prime to "really exploit" denser resolution sensors - new zooms are up to the standard, including top zoom lenses from Canon and Sigma. New primes might go even farther but for practical purposes the zooms are often more than enough - it's a sign how far things have come in a short time (only twelve years, from 1996-2008) that a 70-200mm f/2.8 IS II is actually sharper than the fixed 200mm f/2.8 non-IS.

 

[tjshot]

Also don't agree that you need a great prime to "really exploit" denser resolution sensors - new zooms are up to the standard, including top zoom lenses from Canon and Sigma. New primes might go even farther but for practical purposes the zooms are often more than enough - it's a sign how far things have come in a short time (only twelve years, from 1996-2008) that a 70-200mm f/2.8 IS II is actually sharper than the fixed 200mm f/2.8 non-IS.

I was thinking more about lense performance wide open than pure resolving power: for an APS-C sensor compared to a full-frame one, having to cope with lower SNR ratio for the same ISO setting, a good lense performance at F 2.8 and above can make the difference.
Many recent primes behave outstandingly well in the center up to F 1.4, allowing for the use of optimal low-ISO settings.

 

[AprilForever]

At the level of development we have reached today a small increase of pixel pitch (effective sampling rate -> sharpness and resolution boost) in the sensor will induce a much higher (square growth law) megapixel count, thus requiring much larger in-camera buffer memory, faster data saving channels, more powerful computers etc.

At the same time noise control becomes increasingly difficult (square growth law) due to higher amplification of the signal needed to achieve the same ISO rating; on the other side smaller pitch sensors seem to produce a much more even and defined noise, partly counterbalancing the degradation in quality (think about the terrible "pepper" grain in Canon EOS 5D compared to the smoother Canon EOS 7D).

Solution: We must use round pixels on a round sensor! The square problems will be a thing of the past!!! (actually I have seen something about hexagonal pixels...)

I love more megapixels. And we all should. As the technology progresses, things will get better and better!The 7D is hugely better than the 300D. The future cameras will gradually get better than the current ones. And more megapixels is a part of this growth.