Longer exposures vs ISO with DSLR

[dph1nm]

I'm not sure why changing the ISO changes the balance of noise and signal. But for comparison, all I did was divide the saturation (which you can assume is the signal) by the read noise for each ISO. You can see the results on the tables above under column heading "SNR". You can see with the 6D, it gradually gets worse, but with the 1100D it peaks at ISO200 before it starts to drop off.

Don't forget the noise in the signal! e.g. if you have 76606 e- the SNR is 76606/sqrt(76606) which is about 280. The read noise isn't particularly relevant unless you have a very low signal. I have to say I think the DR values that Sensorgen provide are rather meaningless for the same reason.

NigelM