On 2018-06-14 13:48, Jim-P wrote:
In film cameras, ISO referrs to the sensitivity to light of the emulsion.
Manufacturers formulate different film emulsions with different
sensitivites tarding increased grain with increased ISO speed.

In a digital camera, presumably the sensor does not adjust itself to have
greater sensitivity. Or does it?

So what is happening in a digital camera when I choose a greater ISO
setting? Is more amplification being used?

Typically two stages:

0: the natural ISO of the sensor (whatever value it is - somewhere in
the 100 - 800 range).

1: Analog gain (possibly negative) applied at the time the image is
"read off" of the sensor. This will go up to some limit, eg: ISO 2000
(depending on the model it will be more or less). Noise is amplified
with signal. Analog and/or digital noise filtering may be applied.

2: Digital gain applied to the data after it is read off, before it is
stored on the data card. This has no limit at all except of course
contribution to noise, especially quantization noise. Digital noise
filtering may (and likely is) applied.

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