Ctein over at The Online Photographer is on the job. Or rather, postulating about It, since this is more of a theoretical question.
It being: just how fast can a camera capture light? In the film era, the fastest rolls available at stores were 1600 or 3200 ISO (often something more like 1000 ISO push-processed). These rolls were pretty grainy.Top-line digital cameras can now get decent image quality at 6400 ISO, still-usable quality at 12,800 ISO, and a marketing department claim of 102K ISO to round out the numbers.
But what is the limit? How much faster can photo sensors go?
Here are Ctein's observations on the steps that can take digital camera high ISO speeding into the future:
First, install a back-side-illuminated sensor (unless I misread the specs, the D3s isn't using one). BSI sensors are about twice as efficient as conventional ones at gathering light. Large pixels don't benefit as much as small ones. For the D3S I'd be conservative and call it a 2/3 stop gain (for micron sized pixels, it's distinctly more than one stop).
BSI sensors haven't made big inroads yet, although they're in a few cameras. I suspect a combination of cost and the fact that smaller-sensor cameras need them more desperately.
Next, Kodak has this nifty modified Bayer filter array that gains you another stop of efficiency.
... Couple these two improvements with a 'sensitizer' for the silicon and Ctein thinks cameras can get another 10x ISO improvement, leading pro SLRs up to 1,000,000 ISO in the not-far-off future.
Now that's seeing in the dark.
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