[rogerco (Roger)]

Just started reading Charles Bracken's book "The Deep-Sky Imaging Primer", very interesting read. Question:- early on he talks about the relationship between gain and dynamic range (which I would relate to number of grey tones) and suggests that as you increase ISO (increasing gain) you decrease the dynamic range. In an example he gives a theoretical DSLR where 100 ISO equates to zero gain and 200 ISO indicates a 2x gain.

Now I have a Canon 600D and read through the manual but nowhere can I find anything that discusses gain or any indication that 100 ISO might be zero gain. Do I just assume that because 100 is the lowest ISO setting that that is zero gain?

Anyone with more knowledge than me (just about everyone!) know the answer to this.