Does changing the ISO actually change the sensor...

[sirch]

...or does it just cause the "pixel" values to be written differently?

This is a "I was just wondering" sort of question, obviously changing aperture changes the physical characteristics of the lens and changing the shutter speed changes the time for which the sensor is exposed but what does changing ISO on a modern DSLR do? I can see that it could change some electronic characteristic of the sensor, e.g. change the gain or it could be applied to the sensor data as it is being written, e.g. multiply each value be a factor. Does anyone know?

 

[st599]

It changes the pixel amplifier gain.

 

[sirch]

Thanks @st599

 

[Alastair]

If you really want to give your brain a workout, have a Google for the effects of base/native ISO.. it gets very complicated very quickly, but only really makes much if a difference if you're trying to screw every last drop from your dynamic range.

 

[sirch]

Ahh! OK thanks @Alastair, a bit of Googling seems to indicate it may be a bit of each. The suggestion being that +1EV ISO settings are achieved by altering the analogue gain and ISO's in between are achieved by pushing or pulling (i.e. modifying the values digitally) from the nearest 1EV ISO.

Several people suggest on a Canon ISO 160 is better, noise wise than, 100, interesting albeit a bit academic since it is probably not that noticeable in a finished image.

 

[chris malcolm]

The base ISO is usually taken to be that ISO which gives the widest dynamic range, usually in the 100-200 ISO range. But if what you want is the least noise possible, e.g. to permit the least noisy shadow lifting, and you don't mind sacrificing a bit of total dynamic range, then a lower ISO (if available) can be better.