Where are the limits (resolution, etc...)

[Dan Wells]

I agree that using a sensor at apertures above its diffraction limit will not provide any WORSE results than using a lower resolution sensor running at (or just below) the limit. In addition to the development cost that BJL mentions, there are is another limit to this approach, though. The second issue is that higher-resolution sensors are often not equal to lower resolution ones in other aspects of image quality (such as noise and dynamic range). This will become more acute if sensors with extremely high performance other than resolution (notably Fuji's SuperCCD, potentially also the Foveon three-layer CMOS or some relative) show up in more competiitive resolutions. Both of these unusual designs have some performance advantages, but both are hampered by notably low resolution at present (the Foveon is also hampered by low-end Sigma bodies with a nonstandard lens mount, while the SuperCCD was hampered by body problems until the S5). Imagine the choice between a D3x with a 22 mp conventional Nikon DX sensor, diffraction limited around f6.3, and a  Fuji S6 with a 1.2x crop SuperCCD with 14+14 mp. The Nikon sensor clearly outresolves the Fuji, but at a very limited aperture range, and the Fuji has MUCH better dynamic range. I'd take that "S6" over the "D3x" in a heartbeat, given those specifications. The S6 even offers some advantages over a 1Ds mk III with a 22mp full-frame CMOS sensor. The delay in the 1Ds mkIII may be caused by Canon trying to find a way to make a 22mp sensor with per-pixel performance (noise and/or DR)equal to their existing 17mp sensor.

                                          -Dan

[Ray]

The delay in the 1Ds mkIII may be caused by Canon trying to find a way to make a 22mp sensor with per-pixel performance (noise and/or DR)equal to their existing 17mp sensor.

Dan,
It would be fascinating to find out what ideas and possibilities the guys in Canon's labs are currently working on. Is there an unusual delay between the 1Ds2 and 1Ds3? We have only one precedent here and that's the interval between the 1Ds and 1Ds2. How long was that? I don't see that Canon is under any obligation to bring out new models in a clockwork manner. Also, it doesn't seem good marketing policy to have too many goodies competing with each other for the consumers' dollar. It tends to dilute the return on R&D and setup costs.

The second issue is that higher-resolution sensors are often not equal to lower resolution ones in other aspects of image quality (such as noise and dynamic range).

This only applies when all else remains the same. Perhaps it's odd that no manufacturer seems to have pulled out all the stops to produce a high DR camera at the expense of resolution. Would there be a market for a 6mp full frame 35mm sensor with 16 bit processing and an extra couple of f/stops of DR?

The current level of dynamic range in DSLRs is roughly that of color negative film. Most photographers seem reasonably happy with it, but I agree that Canon does not want to go backwards in this area.

I can't see why there should be an insurmountable obstacle to producing say a 50mp 35mm sensor with noise and dynamic range characteristics at least as good as the current 1Ds2. For dynamic range and noise to remain the same on the same size print, it is not necessary for the smaller pixel to have the same low noise and the same DR as the larger pixel. All that is necessary is to keep noise and DR the same per unit area of sensor, and this could be achieved by reducing read noise and increasing quantum efficiency.

Let's consider what might be involved with our imaginary 50mp camera which would have a pixel pitch of half that of the current 1Ds2. If the light gathering capacity of the 4 smaller pixels in total were equal to that of the one larger pixel and, if the read noise of each of those smaller pixels was no greater than 1/4 the read noise of the larger pixel, then DR and noise would be the same for any given size print, but the 50mp camera would produce higher resolution and more detail on a sufficiently large print.

It might also be possible, as manufacturing processes develop, to place all the photon receptors on one side of the chip and some, if not all, of the processors, such as analog preamplifiers, on the reverse side of the chip. That would allow the photodiodes to be larger within the same pixel pitch.

[Dan Wells]

Has anyone seen a double-sided chip in any application? Interesting idea, and I've seen double-sided (and even multi-layer) circuit boards all over the place, but never heard of an actual chip being double sided...

                                       -Dan

[Dan Wells]

In a sense (although it's not FF), the Fuji S5 is pretty much Ray's "dynamic range at the expense of resolution" camera. It's an $2000 6 MP camera when all other 6 MP SLRs are $500 economy specials. Apparently the dynamic range beats anythine else on the market (including MF backs?)


                          -Dan

[Christopher]

Dan,
It would be fascinating to find out what ideas and possibilities the guys in Canon's labs are currently working on. Is there an unusual delay between the 1Ds2 and 1Ds3? We have only one precedent here and that's the interval between the 1Ds and 1Ds2. How long was that? I don't see that Canon is under any obligation to bring out new models in a clockwork manner. Also, it doesn't seem good marketing policy to have too many goodies competing with each other for the consumers' dollar.

Yes but do you really think they are selling many 1DsMk2 now ? I really don't think so.

[Marsupilami]

Diffraction might be the key point in limiting useful sensor resolution.

Some links with useful reading:

http://luminous-landscape.com/essays/Equiv...s.shtml#another

http://www.cambridgeincolour.com/tutorials...hotography.htm#

http://www.luminous-landscape.com/tutorials/dq.shtml

So far as I have understood it seems valid that from the technical point (year2007) it is not very useful to go beyond 20 MP with a bayer sensor as diffraction increases with the MP count. So the more MP the less useful f stops you have. The only possibility seems a foveon like sensor if you want to go beyond that. And that if we do not look into the issue of corner sharpness with FF at wide angle lenses. I see with my 5D and the 24-70 already a lot of unpleasant corner issues at architecture or landscape shots where I am forced to take at least f 11 to get an acceptable performance.
Which brings me to the question if the next generation of pro SLR cameras are really that better resolution wise. They can bring better DR, better ergonomics and new features like dust remove or live view, but my "fear" is, that if you want top resolution with a decent corner sharpness you have to go the MFDB route - no way for me as I like to shoot outdoors in rough climate and my bread and butter jobs are at dim light (churches).

Christian

[John Sheehy]

Let's consider what might be involved with our imaginary 50mp camera which would have a pixel pitch of half that of the current 1Ds2. If the light gathering capacity of the 4 smaller pixels in total were equal to that of the one larger pixel and, if the read noise of each of those smaller pixels was no greater than 1/4 the read noise of the larger pixel, then DR and noise would be the same for any given size print, but the 50mp camera would produce higher resolution and more detail on a sufficiently large print.[a href=\"index.php?act=findpost&pid=120545\"][{POST_SNAPBACK}][/a]

Actually, to get equal read noise per unit of area, it could double (in ADUs) or halve (in electrons).  Read noise does not add, like photon counts do (shot noise doesn't add, either, it has the same square root relationship).  It's only the photon *count* that adds linearly.

[Ray]

Actually, to get equal read noise per unit of area, it could double (in ADUs) or halve (in electrons).  Read noise does not add, like photon counts do (shot noise doesn't add, either, it has the same square root relationship).  It's only the photon *count* that adds linearly.
[a href=\"index.php?act=findpost&pid=120714\"][{POST_SNAPBACK}][/a]

John,
Thanks for mentioning that. So in order to keep total image noise the same with 4x the pixel count on the same size sensor, each of the smaller pixels of half the pixel pitch, should have half the read noise. Right?

Would I be right in thinking that photonic shot noise should remain the same, irrespective of pixel count, provided that the same number of photons are reaching the same area of sensor, or does photonic shot noise for the whole image double in this situation of 4x the pixel count?

[Ray]

Yes but do you really think they are selling many 1DsMk2 now ? I really don't think so.
[a href=\"index.php?act=findpost&pid=120570\"][{POST_SNAPBACK}][/a]

Probably not. The star performer is currently the 1D3. A 1Ds3 would not be a competitor to the 1Ds2 (which would become a discontinued model) but the 1D3.

[Ray]

So far as I have understood it seems valid that from the technical point (year2007) it is not very useful to go beyond 20 MP with a bayer sensor as diffraction increases with the MP count. So the more MP the less useful f stops you have. [a href=\"index.php?act=findpost&pid=120583\"][{POST_SNAPBACK}][/a]

This seems to me a misconception. Diffraction is a property of the lens. Until we succeed in producing matamaterials with a negative refractive index, suitable for camera lens construction, there's not much we can do about it without resorting to cumbersome techniques. There is no disadvantage in having a sensor which can outresolve a lens at a particular f stop. You won't get worse resolution at f16 because your sensor has more pixels than are needed.

There has always been a trade-off between getting maximum resolution and getting the desired DoF. It stretches across all formats. Large format photographers try to get around this by using tilt lenses. You can also use tilt and shift lenses with Canon 35mm DSLRs, but the TS-E 24mm seriously needs to be upgraded in my view.

There's also software currently available which can successfully merge a number of shots which have been bracketed with respect to focussing. This seems to me a process which could have great potential. Imagine, you have your 50mp DSLR on a sturdy tripod. You are using Canon's latest, highest resolving prime lens which is as close to being diffraction limited at f4 as most current lenses are at f8 (ie. double the resolution at the same MTF). The camera supports focus bracketing at up to 10 frames per second. You focus on the furthest point you want in focus, press a button; focus on the nearest point you want in focus, press a button; dial in the number of intermediate focussing points you need (or maybe the camera can work that out); press the shutter and voila!.

[juicy]

Hi,

To add to BJL's
 

The worst that can happen to image sharpness and detail is that higher resolution only gives a useful improvement in resolution in a very limited range of cases, of rather large apertures and low DOF (with low DOF made more noticeable by the greater enlargement and or closer viewing used to see the extra detail.) Not that performance is worse than with a lower resolution sensor at small apertures, or that small apertures cannot be used at all.

and to Ray's

There is no disadvantage in having a sensor which can outresolve a lens at a particular f stop. You won't get worse resolution at f16 because your sensor has more pixels than are needed.

views I'd like to remind (although already discussed in earlier threads) of the possibility of getting along without AA-filter in the case of a sensor with high enough resolution. Personally I like 1Ds very much, it gives very sharp RAW-files because of a relatively weak AA-filter. The downside of it is of course the moire issues. Even Canon's WA-zoomlenses at f14 are sharp enough to introduce moire in 1Ds on certain subjects like scenes with far away office buildings with finely detailed vertical/horizontal structures. We have also seen moire issues in similar subjects when using 30+ megapixel MFDBs with sharp lenses.

In this sense I think we are not yet very near to the true limits of usable sensor resolution. Different topic is if the file sizes, noise characteristics and manufacturing costs etc are in reasonable relation to the potential IQ gains. Also for the added resolution to be fully exploitable the user has to be ever more careful in his/her technical craft. Except for the corner performance of many WA-lenses I think there's still quite a bit of room for added sensor resolution that can be put to use. Especially when making large prints it has always looked better to have camera-creted pixels (no matter how diffraction limited) than to have interpolated pixels.

Cheers,
Juicy

[John Sheehy]

John,
Thanks for mentioning that. So in order to keep total image noise the same with 4x the pixel count on the same size sensor, each of the smaller pixels of half the pixel pitch, should have half the read noise. Right?

Right, relative to signal.  

Would I be right in thinking that photonic shot noise should remain the same, irrespective of pixel count, provided that the same number of photons are reaching the same area of sensor, or does photonic shot noise for the whole image double in this situation of 4x the pixel count?
[a href=\"index.php?act=findpost&pid=120728\"][{POST_SNAPBACK}][/a]

Shot noise is a function of quantum efficiency and exposure, only, per unit of area.  Pixel-wise, it doubles (relative to signal) when fixing exposure and QE, but quadrupling the pixels per unit of area.

[Ray]

Right, relative to signal. 
Shot noise is a function of quantum efficiency and exposure, only, per unit of area.  Pixel-wise, it doubles (relative to signal) when fixing exposure and QE, but quadrupling the pixels per unit of area.
[a href=\"index.php?act=findpost&pid=120776\"][{POST_SNAPBACK}][/a]

Okay! To get back to the hypothetical 50mp FF 35mm sensor. If I've understood you, such a sensor would have double the shot noise (over-all) as well as higher read noise compared with the 5D, provided we're talking about the same technology, same quantum efficiency of each pixel, same light gathering capacity per unit area, same read-out precision etc.

As technology advances in all related areas, it seems reasonable to me that such disadvantages will be overcome. The pixel pitch of such a 50mp camera would be around 4 microns, not much smaller than the pixel pitch of the latest 4/3rds DSLR from Olypus, the 10mp E-410 Volt with a pixel pitch of around 4.7 microns.

All Canon has to do to make such a 50mp camera worthwhile is design a few 35mm lenses of equal quality to the Zuiko lenses   .