Quote:
Originally Posted by whzzz28
So what am i better off doing:
a) 1600 ISO for 300seconds, 10 subs or,
b) 800 ISO for 600seconds, 10 subs or,
c) 800 ISO for 300seconds but take double the amount of subs (20)
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As far as I am aware from trolling through all the mathmatics when I was using a DSLR. The ISO reading does not make any difference to the signal generated.
If you think about this it makes sense, in film cameras the ISO would make the film more sensitive to the light but in DSLR photography this is not possible. ISO cannot make the sensor more sensitive. It also cannot make more light hit the sensor, so what it does is amplify the signal. This also amplifys the noise and you end up with a situation like tlgerdes suggests, 10 noise and 100 signal at iso 400 would go to 100 noise and 1000 signal at iso 4000.
Using the above example it would suggest that the lowest amplification factor is best (iso). But it turns out that the iso rating of a camera changes its internal noise. For this reason there is a optimal ISO rating for each camera that has the lowest noise. The theory suggests that you should always use this optimal iso rating for the best SNR images.