Is the difference between STD2 and STD3 gammas just the blacks?
For me STD2 seems to be cleaner than STD3. I know STD2 has deeper blacks and it may be the reason why it looks cleaner. But is that the only difference? As of lately I have been shooting all my green screen work using STD2 because of it being cleaner but I used to shoot green screen with STD3. So I'm just trying to figure if it was a smart decision in switching to STD2. Thanks.

If it works for you and looks cleaner then use it. STD 3 is the closest EX gamma to Rec-709, the standard gamma for HD video production so should give you the most natural looking images on a regular TV or monitor. As you have observed gamma 2 does compress blacks and mids somewhat compared to 3 and this is indeed why it looks cleaner.

Thanks Alister. Do you think I am losing anything because of the compression of the blacks and mids even though I'm in a totally controlled environment, meaning a studio situation where I have full control of my lighting?

You will be loosing some black detail. If you going to grade you would be better of using Standard 3.

Yeah, I will definitely grade.

But I thought as long as I exposed the shadows properly, meaning not let them get clipped and go too black I would be fine? I did that mainly to avoid noise which is a big problem in green screen. As long as I expose the shadows "properly" would I really lose detail in the blacks?

By crushing or squashing the blacks into a smaller range you are using less data to record them, so any stretching in post will reveal banding and other compression artefacts sooner.

Thanks.
I realize that. But as long as I light my shadows bright enough and do not need to lift them up in post (this is what you mean by stretching right?) I should be fine then?
Just want to make sure we are on the same page and that I'm not missing anything.

Correct. Stretch/lift similar things. You don't seem to be missing anything at all.

If anyone finds my marbles, I'd be pleased to hear.