As I have said before, methods already exist to essentially eliminate the effects of well capacity limits; for example, reading out each well as it approaches being full. Most of your arguments crumble once that is achieved, because it is not possible for a larger format to offer better than the UNLIMITED highlight headroom and dynamic range of a smaller one.
BJL,
Are you absolutely certain about this ?
The central part of my argument got lost somewhere. It's this. I agree that the application of much technological wizadry could eventually create a small camera capable of outstanding performance on a par with what we currently get from bigger DSLRs and even what we hope to get in the future from DSLRs,
but only if the research dollars go in that direction and cease to flow to further development of the larger format cameras.
The argument that this appears to be what is happening and that large format digital cameras will eventually cease to be economically viable and become dinosaurs, is another issue.
I am merely concentrating on the inherent potential of two hypothetical formats that differ greatly in size. In relation to
that argument you are making some controversial statements, the logic of which I find difficult to follow.
Let's get down to some more examples using simple maths. Compare two sensors of equal pixel density but the smaller sensor has 1 micron photosites and the larger sensor has 10 micron photosites. The smaller camera has an f1 to f4 lens. The bigger camera has an f4 to f32 lens. DoF at f1 on the smaller camera is equal to DoF at f10 on the bigger camera. Both sensors have eliminated all dark noise. Photon noise is the only noise.
What you are proposing, if I've understood you, is that we could completely sacrifice the speed advantage of an f1 lens by using the same exposure duration that the larger camera would use at f10. As soon as a photosite is full, the charge is read, transferred, dumped (whatever) but essentially noted. The fact that pixel #1124 was filled 200 times during a 1/100th sec exposure and pixel #13 only once, is recorded and used to construct an image with full dynamic range.
This is a great idea, but suppose the larger camera adopts the same technique?
Here are what I think the issues are.
(1) Nothing happens instaneously (except perhaps in fictitious quantum computers using qantum entanglement). In practice, if we want to get that photosite #13 to fill just once (representing the darkest part of the image) it is going to take a somewhat longer exposure than the larger camera would use at f10. This effectively means the smaller camera would have optimal performance at say ISO 64 as opposed to ISO 100 for the larger camera. So already the larger camera has a speed advantage at equivalent DoF before we've even applied this amazing technology; the opposite of what we're used to.
(2) But the big issue is the significance of the far lower S/N of the bigger sensor. To refresh, 1000 electrons at full well have 33 electrons of photonic noise. 100,000 electrons have only 317 electrons of photonic noise.
If we employ this same technique with the larger camera,
we don't need to wait until the well is full. For the same Signal-to-Noise, we can set the camera to transfer the charge (or note the charge) when the well reaches 10,000 electrons (1/10th full well). This effectively means we get the same DR performance of the smaller camera,
but at a yet higher ISO setting.
And we haven't even begun to consider the benefits of those diffraction limited F4 lenses on the bigger camera, which I surmise would be ideal for noise-free hand-held shots at ISO 128,000 (or even higher) in the Vatican Museum .
Let's face it, BJL, these tiny digicams, however sophisticated, are just toys for the consumer mass market .
Note, I'm jumping in here a second time to correct my maths. Such gross errors are intolerable (no calculator at hand). I figure 33:1000 is equivalent to 317:10,000. The bigger well, 100x the area, needs to be only 1/10th full to match the S/N of the smaller well; ie. we can get the same results at f10 using
less than 1/10th the exposure, combining points (1) and (2).
It can be seen if we start using F4 on the larger camera, the ISO benefits (shutter speed) are enormous.