Wade, I understand the logic, but I do suspect the longer integration time of gain 0 does have more data. I guess the question you are proposing which option is better. My intuition tells me the following would be nearly equivalent.

Gain 0 *does* have more data. Since the gain 0 exposure is longer, the sensor has literally received more photons.

Where it gets confusing is that gain 0 also has more *read noise*. This read noise is fixed, independent of exposure length. And it wipes out the faintest details. To pull the faintest details out of that read noise, you *need* to expose longer at gain 0.

When you use gain 100, you don't have to expose at long to get the faint details. And the shorter exposures tend to reduce the tendency of bright stars to saturate.

When you do the math to calculate the dynamic range, it turns out that when you account for read noise, a shorter exposure at gain 100 is nearly an identical equivalent of a longer exposure at gain 0. The pixel values in the longer exposure will be higher, but when you account for the additional read noise, you could do a division operation on the longer exposures to make the pixel values equivalent to the shorter exposure. After doing that, the two exposures will be nearly the same in every way. You would not be losing faint details in the division operation, only noise.

Gain 0 - 240 subs at 120" (4 hrs) of luminance

Gain 100 - 480 subs at 60" (same 4 hrs of data)

Intuitively I do not believe that 2 hours of gain 100 will equal the 4 at gain 0. Happy to be proven wrong.

I am not saying that 2 hours of gain 100 is equal to 4 hours at gain 0. I've not bothered to calculate the equivalence.

I *am* saying that if you compare identical exposure times at gain 0 and gain 100, the gain 100 subs will have higher S/N. That should be quite easy to prove to yourself through experimentation.

The rest of my argument is qualitative, not quantitative. Honestly, keeping it qualitative is 100% me being lazy. I have some other stuff that I need to get done today, so have not looked at the math. Other than the math on the ZWO chart data, my math has been done with hypothetical numbers, chosen to make it simple.

If people would like, I can take a look at doing a quantitative analysis to determine the actual exposure equivalency when I get a chance. It would likely not be today, though (unless I have a breakthrough in my other task for the day)...