But as I said above, the overall scaling between photosite size and total dark noise is not clear, so the "winner" here is not clear either.
What I find interesting here is that dark noise is subject to technological strategies for improvement even if it requires a certain degree of internal cooling (which wouldn't necessarily be difficult with a really tiny camera housed in a much larger body so one can hold the thing).
Photonic shot noise and diffraction limitations seem to be the ultimate barriers to small cameras producing high quality, high resolution images.
I take the point that averaged multiple exposures might reduce the randomness effect of misbehaving photons (you can see I'm not very technical) but I suspect not by much.
Photon noise is proportional to the sqrt of the number of photons impinging upon the photosite. Ie., if the photosite receives 100 photons, noise is 10 photons, or 10% of the signal. If 1000 photons are received by the photosite, noise is represented by a mere 32 photons, about 3.2% of the signal.
Is this a limiting factor as draconian as lens diffraction limitations?
I made the comment that maybe soon we'd have an ultra-small camera capable of matching the DoF of a pinhole camera but with razor sharp images. I can't really see it unless these basic laws of Physics are repealed. (Perhaps the new Pope can do that. Oops! I apologise in advance in case anyone deeply religious is reading this
).
To clarify the problem, I designed an imaginary small camera to compare with FF 35mm in terms of DoF and resolution. Using the wavelength of red light as the limiting factor for pixel size, and allowing for the usual discrepancy between pixel pitch and pixel size, I used a 1 micron pixel pitch on a 4.5x3mm sensor (keeping the same aspect ratio as 35mm).
Such a sensor would have 15MP and a standard lens, equal to the diagonal of the sensor, would be about 5.4mm in focal length.
To get the same DoF and resolution of a 35mm camera at f8, we'd need a diffraction limited f1 lens. (Not possible now maybe, but with the help of nanotechnology and improved materials, maybe sometime.)
This would clearly be an amazing camera for any subject that requires a reasonable DoF, but with one serious limitation; dynamic range. I can only guess what that might be; 1 stop of undegraded DR described as 3 or 4 stops by the advertisers of such a product?
Let's assume such a camera has just 1 stop of 'clean' DR. To get a DR of 8 stops, we need to blend 8 exposures, the shortest of which for the highlights (which at F1) might be around 1/25,000th of a second on a sunny day. We progressively halve that shutter speed for each of the 7 remaining stops till we reach 1/200th sec for the deep shadows. Bingo! We've got the full DR of a modern DSLR, and more perhaps.
But what about DoF? Well I'm afraid we're stuck with the limitations of diffraction. With such a camera the hyperfocal distance is around 24ft whether it's a 4.5x3mm sensor at 5.4/F1 or a 36x24mm sensor at 43/f8.
Supposing we want a really great DoF comparable to that of a pinhole camera but at the same time
sharp. Perhaps we could reduce the aperture opening from F1 to f8 on our miniature camera.
The DoF calculator I've been using at
http://www.dofmaster.com/dofjs.html tells me that such a camera I've designed, at f8, will produce a sharp image from 1.5ft to infinity (CoC 0.004 proportional to the program's fixed CoC of 0.03mm for 35mm format). Whatever CoC standard is chosen, the relevant multiplying factor is 8 and the results are the same.
Okay! The assumption is, the lens at f8 can transmit that resolution. Well, of course it simple can't because of diffraction. The sensor in my designed camera has at most a theoretical resolution of 500 lp/mm, but a paractical resolution of maybe 400 lp/mm with a diffraction limited F1 lens. (Guess work of course).
Any image at f8 on such a camera would be no sharper than a 35mm shot at f64.