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Anonymous
>>260207 cont'd
The fundamental difference between film and a digital sensor is that, with a sensor, a single device has to work at all sensitivities. The photon wells are a set size, and the amount of light coming in is a constant for a given ISO equivalent (remember above). The next crucial thing to notice is
- no matter the size of the photon wells, a camera at a given ASA equivalent must always react to the same amount of light -
So your camera is sitting around set to ISO 25000. You take a shot, and a tiny number of photons squirt in, equivalent to the number needed for a proper exposure at that ISO. They go into these massive photon wells designed for shooting at ISO 50 and sit there at the bottom. The only way that having larger wells improves noise characteristics is by integrating the photons over a larger area -- the other key factor in noise production is, obviously, the lowest ISO the camera was designed for!
Basically, because these photon wells are so underfilled, there's always going to be a terrible signal-to-noise ratio. If your camera had a base ISO of 1600, then the wells would only need to be deep enough for that level of light, and ISO 25600 would be that much closer to a "full" exposure of the wells. When your camera sensor has to react to an enormous range of photon levels, increasing the frontal area of the sensors can only do so much to improve noise characteristics.
In essence, Canon has recognized this and is doing something else to improve noise (and they really are, just look at these photos). Incidentally, the idea that you can shoot ISO 3200 basically noiselessly is stunning to me, since Delta 3200 is pretty much a mess of grain.
TL;DR: Increasing the size of the sensor sites will only work to improve noise to a certain extent, and if you really want high ISO performance, you're going to have to give up the low end in exchange.
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