Top-end digital concerns

[Clement Apffel]

After a lot of time spent reading technical reviews and articles, I still do not understand some of the major concern of current digital hardware.

My main interrogations are about the physical size of pixels:

In the first hand we have very respectable theoretical calculation about the diffraction related with the diameter of the pixel size. Those calculations bring us to many known facts like those:

Under the size of 9 nanometers, the image quality falls quite hardly. The ratio signal / noise forces to use heavy corrections in the DSP.

With a given pixel size, you won’t be allowed to close your aperture more than a given value under which the size of the Airy disc becomes greater than 2 pixels diameter and makes the capture quality fall drastically.
This value is known as being 2.12*pixel size (in nanometers)
Example: the Canon EOS 5D has 8 nm pixels. 2.12*8=16.96. that means that you can’t close your diaph under f/17. and that is not related to focal length nor CCD size. It is just a plain relation between pixel size and Airy disc diameter.

And on the other hand we have gear producers that continue the Mpixels race.
In February 2k8 Sony announced its 24.6 Mpixel 24x36 mm CMOS and few month later Nikon uses that CMOS in its D3x.
That is 6.4nm pixels.

Digital backs show pixel size between 5 and 7 nm too. And one wouldn’t be a fool to bet on the fact that future releases will show more pixels on same sized sensors.

So what is all that about? I’m getting confused.
And one can find almost none field feedback about those aperture / pixel size problem. It doesn’t appear to be a well known technical issue.

Is it just theoretical hair splitting ?
Is it just commercial big numbers war unrelated with the image quality?
Do I miss something big somewhere?

I guess that the DSP corrections are getting better and better. But does that mean gear producers renounced to perform optimal capture and few corrections in their devices?

I can understand that a 300$ point and shoot camera is designed with 3nm pixel size, cheap sensor, plastic lens and MASSIVE DSP corrections.
But what about top-end professional digital gear?

With film, I have a 100% control on gear, film, processing and almost a 100% understanding of each.

To me it is very frustrating to use or be forced to use a gear that I do not fully understand. (digital MF/LF devices)
Not knowing and not controling what happens in the magic box (DSP), not knowing the technical trade-offs that are made by gear producers on sensors is unacceptable to me.

So that is why I would like to start a discussion of this kind on my favourite photography forum.


I am aware that this topic is not 100% related with LF. But I didn’t feel like starting this thread in the lounge!
Moreover it is about current concern on photography. And my worry in this topic is top-end quality just as in my LF work and LF topics.
And finally I am curious to read the opinions of the experienced photographers and the optics experts roaming on that forum.

Regards,
CA.

PS : I hope my english isn’t too much of a pain to read.

[Aender Brepsom]

Hi Clement,

my answer will not satisfy you at all, because I am quite the opposite of you regarding technical details. I don't invest my time in understanding all the technical aspects of a DSLR camera, but just use it as a tool for my purposes. There are limitations, but compared to 35mm film, a camera like the 5D or the 1Ds Mark II/III has nothing but advantages. With 35mm lenses, you couldn't stop further down than f/16 either without getting diffraction issues. This is not different with FF DSLR bodys.
Again, I do not care much about technical details, but I just see the excellent results from my 1Ds III and that is enough. For me, with prints up to 1m large, the only (but very important) advantage of LF over DSLRs are the movements. If I could have the movements on a DSLR (more than with a few tilt-shift lenses), I probably wouldn't use a LF camera any more.

[Noeyedear]

Hi Clement,

my answer will not satisfy you at all, because I am quite the opposite of you regarding technical details. I don't invest my time in understanding all the technical aspects of a DSLR camera, but just use it as a tool for my purposes. There are limitations, but compared to 35mm film, a camera like the 5D or the 1Ds Mark II/III has nothing but advantages. With 35mm lenses, you couldn't stop further down than f/16 either without getting diffraction issues. This is not different with FF DSLR bodys.
Again, I do not care much about technical details, but I just see the excellent results from my 1Ds III and that is enough. For me, with prints up to 1m large, the only (but very important) advantage of LF over DSLRs are the movements. If I could have the movements on a DSLR (more than with a few tilt-shift lenses), I probably wouldn't use a LF camera any more.

Strange how people see things differently. I also have a 1DsmkIII, I'm sort of disappointed with it, not that it does not perform very well, it does mostly. It leaves me thinking it should be better, hence a return to LF for me for the fun side of photography. The more pixels I have in 35mm cameras the more I like film. I've not found any Canon lenses to get me excited either. The latest range of pixel packed 35mm just leave me cold, all those pixels help highlight digital faults and make me realise how good film is and how I took it for granted.

Kevin.

[Stefan Lungu]

Strange how people see things differently. I also have a 1DsmkIII, I'm sort of disappointed with it, not that it does not perform very well, it does mostly. It leaves me thinking it should be better, hence a return to LF for me for the fun side of photography. The more pixels I have in 35mm cameras the more I like film. I've not found any Canon lenses to get me excited either. The latest range of pixel packed 35mm just leave me cold, all those pixels help highlight digital faults and make me realise how good film is and how I took it for granted.

Kevin.

Now, I don't think getting the 1Ds MKIII is not a good idea, unless you have the lenses to serve that fully packed sensor. So a dedicated photographer like yourself will be disappointed with most of Canons lens offering. But the talk here made me think : I started using a Canon 300D, 6Mp sensor. Now, to be able to double the frame length, I need four times more pixels, and that would be around the new 1Ds MkIII or 5d MkII. That is a hell of a leap in years and price, not to mention the lenses that looked "ok" or "good" on that sensor compared to how they would look like on the 20+MP sensors. I think a lot of the problems come from this never ending pixel race that brings nothing but trouble to the end user : artefacts from the noise reduction that has to be bigger with the smaller pixels, larger files and better lenses that are needed to get something right on that sensor.

[bglick]

> I think a lot of the problems come from this never ending pixel race that brings nothing but trouble to the end user : artefacts from the noise reduction that has to be bigger with the smaller pixels, larger files and better lenses that are needed to get something right on that sensor.


This is soooo true, well said..... its like Pandoras box. :-) However, part of the discussion here addresses this.... don't let the pixels get too small, by increasing the size of the sensors...you still need good lenses, a step better than most LF lenses, but its a very good solution... the deterrent is only price, such as the $40k P65, 60MP backs. The big question is, will these ever become reasonably priced?

HD Tv's were $15k in 1997, today, $1k.... We have all become accustomed to these technology price drops...even Sony at $3k for 24MP is setting new price bars. Whether this happens with larger, lower volume sensors...who knows... my guess is, the volume is just too low to ever get the price reductions that will make MF backs more mainstream.

[Emmanuel BIGLER]

Hi Clément

Following your post, the question relevant to large format users are
- since digital is supposed to deliver better images than film with he current "35mm" (24x36mm) and medium format silicon sensors (now close to the 41x56 = 645 film size), with a better work-flow and (hopefully) with a better cash-flow (for professionals), is there any future for even 6x8 cm silicon chips and above ?
- if large format silicon chips appear, the question of 3 micron pixel size is less important provided that we have enough pixels to saturate even a one terabyte hard disk with 2-3 images

Regarding smaller pixel size, we should always make a difference between
- pixel pitch or pixel grid periodicity, commanding the rules for the sampling theorem
- pixel surface, commanding the number of photons per exposure for a given illumination and exposure time, hence commanding the physical signal to noise ratio.

Sure, in Bayer patterns both pitch and aperture size are related for practical reasons, but both phenomena are formally different. Reminder : the commercial pixel count for a Bayer pattern is the total number of pixels all colors combined, in fact the actual pitch for red pixels is twice as big as the basic Bayer pattern pitch.

I see a great deal of interest in tiny subpixels as exposed below.

Regarding the sampling theorem I prefer not to speak in terms or Airy disks but in terms of cut-off period or cut-off spatial frequency.
With film we are in a situation of the cut-off period of best films is far above what can pass through a top-class large format lens. So in a sense, all LF users are very happy with a detector which is much better than the lens ! So why not the same for digital photographic imaging, not only for military or aerospace use (or both ) ?

The absolute cut-off period for a diffraction-limited lens si N*lambda where N is the f-number and lambda is the average wavelength of visible light ; in fact taking the worst-case at 0.7 microns (the actual limit of sensitivity fr the human eye) we get an ultimate cut-off period of 0.7 N.
The sampling theorem states that you need 2 samples per optical period to avoid aliasing and moiré effects.

Take a state of the art view camera lens, e.g. a solid modern 150mm for 4x5", consider that it is diffraction-limited at f/16, the diffraction cut-off period is about 11 microns (0.7 * 16), the corresponding cut-off spatial frequency being about 90 cy/mm, a figure hardly reached by any view camera lens covering the 4x5" format. Modern color film are capable of recording fine details above 100 cy/mm but with a vanishing contrast.

I recenty read that Sony has announced silicon chips for mobile phones with 12 Mpix on a sensor with 7mm of diagonal, 3288 x 2468 pixels ; this yields a pixel pitch of 1.7 micron (we know nothing from these figures about pixel surface, smaller than 1.7 x 1.7 micron square !)
http://mobilearsenal.com/new/sony_12...r_mobiles.html

So a pixel pitch of 1.7 microns yields a cut-off period of 3.4 microns, this corresponds to a diffraction-limited lens at about f/5. For a fixed-focal length for a mobile phone, if it is not a wide-angle, why not ? But sure, we are now entering a situation where the optical diffraction cut-off frequency of the lens is the actual limit.
To me this is a blessing since in this perspective we can forget about anti-aliasing filters. Good by also to anti-moiré post-processing software as advertised by Hasselblad !

Compare with the situation we have in LF on film.
If you read the actual MTF data of a fine-grained color slide like PROVIA 100F, you find that the MTF curve of this film is very close (up to 60 cy/mm) to the MTF curve of a 7-micron pitched sensor fitted with an anti-aliasing filter cutting off at 70 cy/mm, except that film transmits fine details with a low contrast well above 100 cy/mm.
Since you are French you can read my article here and check by yourself.
http://www.galerie-photo.com/film-co...esolution.html

But we can use (B&W) films for which the MTF extends above 200 cy/mm, the Gigabit(TM) film was available in 4x5" ! So why not doing the same with digital sensors ?

Regarding tiny pixels, I see a great interest in them since it gives a total freedom to the digital imaging software engineer to do as much pre-processing as thay can inside the camera, or inside the digital back before delivering the actual image file to the end user.
Once the software is developed, it is costless to duplicate it. And the computations are secret and proprietary, do not expect any details about that.
In Europe we do not recognize software patents, so all pre-processing tricks, at least for the European market, will be secret know-how. And if a company is issued a software patent for digital image pre-processing valid only on the US, taking into account that you have to disclose a minimum of technical details in a patent, this would mean that the patent is kept secret for European readers !

So on the contrary I'm expecting that zillions of tiny pixels will continue to be both a marketing gimmick for the years to come, and a blessing for software engineers. It will give them so much freedom in pre-processing, that the question of the optical diffcation cut-off frequency wil be more or less marginal.
I'm thinking of all kind of intelligent pre-procesing software based on smartly combining pixels together, in a adaptative way, testing locally the shapes and intensities in the image, in order to reduce noice where it is the most visible and to enhance egde sharpness ad libitum.
Instead of good old Fourier methods based on a spatially invariant linear processing, I see a heavy use of all kinds of non-linear and adaptative image pre-processing techniques based on brute-force methods with zillions of pixels !

[neil poulsen]

You're taking an interesting approach to this problem. As attracted as I am to technical detail, I'm taking a more emperical approach to this question. But, this may be all the more appropriate, since my interest is more in the low end.

I've been doing a lot of reading, and here are a couple of conclusions that I've drawn:

As for 35mm DSLR full-frame cameras, the current high-end DSLR's in the low 20's megapixels offer about as much resolution as current, high-end DSLR zoom lenses can handle. Maybe one can go a little higher with fixed focal length lenses.

I spoke with Schneider LF technical people, and it was their opinion that at 22 megapixels, one could use traditional LF lenses and not expect to gain that much by "upgrading" to the Digitar type lenses. (I'm thinking in particular of the Mamiya 22mp digital back.) They emphasized that a lot could be accomplished, size-wise and otherwise with a back like that. Above 22p, they recomended more sophisticated lenses.

So, given the expenses involved, this is the direction towards which I'm heading. 22mp can do quite a lot. It'll take a while, but at least I have a plan. While I found an older style Arca 6x9 camera for a reasonable price, I've recently run across a way I can adapt this back to my 4x5. Etc.

About three and a half years ago, I purchased the only full-frame camera that I could afford. There were only two: the Canon 1Ds and the just discontinued Kodak DSLR in either a Nikon or a Canon mount. I wanted to use a 24mm PC lens, so I needed full frame, to get the best wide-angle advantage of that lens. Given the hefty discount, I chose Kodak in a Canon mount. It has it's weaknesses and strengths. It's low ISO, but I use it only on a tripod like a VC. One thing I like, it has no anti-aliasing filter. This gives it excellent color and resolution characteristics. (Until moire interferes.) One advantage to this camera, is that it's good preparation for using a digital back, since they also do not have anti-aliasing filters.

But, there are negatives with the 35mm DSLR approach. Movements are more limited, given the few number of lenses that can be PC controlled. The exposure chamber is small, so DSLR's are more subject to flare,especially in overcast situations. (I hate flare!)

Digital is expensive. A I kind of implied, the direction I'm taking is more driven by what I can achieve, what's available, and a principle of diminishiing returns as one scales the digital ladder.

[Gordon Moat]

A short time ago I commented upon this exact aspect of sensors, yet there were no responses:

http://www.largeformatphotography.in...1&postcount=21

The main issue really is the pixel cell site dimension. While I think a near 4x5 sensor could be possible, there would not be any advantage in having it near 6µm pixel sizes. Without doing the math on this, I would propose that 9µm might be a reasonable limit, and allow some usable apertures and image quality.

One could cram even more pixels into a sensor than can be found on a Nikon D3X, but to do so would sometimes be even more of a compromise of image quality. It would also mean that smaller apertures would degrade image quality even more.

Another possible approach would be doubling of cell sites; imagine a future D6X with close to 52MP sensor. The only practical way to do that would be to double up (or more) the captures, then interpolate into a smaller result. A few small video cameras do that; they have sensors near 5MP and group together four or more adjacent pixels to create a more sensitive signal to produce a lower resolution HD result.

However, I think that the current D3X really is at the performance limit; to go further would have extremely low improvement in optical resolution (not file sizes). I really feel that with the Canon 1Ds Mark III and Nikon D3X, those companies need to concentrate more on improving colour and sensitivity, and give the uberMP race a rest for a while.

Ciao!

Gordon Moat Photography

[Eric Leppanen]

...I think that the current D3X really is at the performance limit; to go further would have extremely low improvement in optical resolution (not file sizes). I really feel that with the Canon 1Ds Mark III and Nikon D3X, those companies need to concentrate more on improving colour and sensitivity, and give the uberMP race a rest for a while.

Thom Hogen seems to reach the same conclusion in his review of the D3x (http://www.bythom.com/nikond3xreview.htm). Some excerpts:

...I would say that f/11 is that last aperture you can use and still have an expectancy of getting near maximal resolution (a term I loosely used before: diffraction limited aperture). Go smaller than f/11 and no amount of careful sharpening will restore the semblance of acuity at and near the Nyquist limit. Moreover, you'll lose signficant contrast, and most people perceive contrast in conjunction with sharpness (i.e. more contrast is perceived as "sharper"). If you're a stickler for detail, don't stray past f/8...For my landscape work, I won't be afraid to use f/11, but if I can get to f/8 I will.

...Indeed, I think that the serious landscape shooter almost certainly needs to consider using the PC-E lenses on his D3x and using the Scheimpflug principle to get depth of field, not solely aperture. If you need to go to f/16 for depth of field in your landscape work, I'm not so sure that you shouldn't just use a D700 and use panorama stitching to get more pixels, despite what that means for moving subjects.

Since I know from 35mm film experience that I can't get traditional near-to-far landscape compositions in full focus at f/8 (and frequently not even at f/11), it would seem that to achieve optimal landscape resolution with a 20+MP DSLR kit, I'd be limited to three tilt/shift lens focal lengths (with limited coverage compared to their LF film counterparts); above and beyond that, I'd have to shoot planar or limited depth-of-field subjects. A lot of folks are perfectly happy shooting 4x5 film with just three lenses (90, 150, and 240 are roughly comparable to the DSLR tilt/shift focal lengths), but I'm not. And stitching is of limited appeal since most of my subjects involve moving objects.

So it would seem that 35mm DSLR's can intrinsically achieve some LF film landscape photography objectives, but not all; and that further ratcheting up the megapixels will achieve little to no benefit due to diffraction. Apparently the only way in the foreseeable future to achieve all LF film camera capabilities with digital capture is to use a technical camera with a digital back. A used 22MP digital back can be cost-effective if one is happy with a maximum 16x20" print size (it would yield roughly 260DPI, which is close to the optimal 300+ DPI used by most inkjet printers), or can shoot subjects amenable to stitching. But the higher capture resolutions required for larger native print sizes are just not cost-effective at this point.

The potential of digital capture is certainly intriguing (the faster shutter speeds by itself would enable a variety of shots not possible with LF film), but for now I'm waiting until the MF digital market shakes out and prices come down quite a bit. And with a deep recession underway, that could take a long time.

[Lenny Eiger]

Clement,

I think there are a lot of numbers out there. Some of them mean something and some of them don't. For commercial work, the convenience of digital and the small target size (magazine page) make it very easy to choose - for most.

I am a fine artist, and I like to print up to 40 inches, in black and white. There is no digital camera that comes close to my needs. I use an 8x10 camera and when I drum scan the image I have a 568 megapixel file. (24, 39, 50, mgpxls is no comparison.) I tried going down to 4x5 (and 6x7), I have a scanner that is exceptional, and should be able to make a file that equals an 8x10. It clearly doesn't. It isn't a matter of numbers. In my case its more a matter of film "real estate".

If print quality is important to you in your work, and you print larger than 15-20 inches on occasion, then film might be a good option.

I would say you might want to rent a top end digital camera for a day and see what it can do. Get a high end drum scan of the same image and compare, with your work in mind.

Lenny