I am at 6000 or 8000 if absolutely necessary

6400, work in 160, 320,640,1250,1600,3200,6400.

Dan, another way of answering your question...

I've been told it's always better to raise ISO in camera then try to boost in post. The reasoning is that high ISO might be ugly, but boosting in post is even uglier. I don't know whether this is true or not.

But if it's true, the answer to your question is there's no max ISO. If you absolutely have to shoot, ie it's a bridal waltz in darkness or whatever, you should raise ISO till you get best possible exposure.

Denoiser II and Neat Video can be VERY helpful when shooting at high ISOs. They slow down export time by quite a bit but they can make noisy footage look so much better.

Whatever it takes to get the video. Better to have something than nothing.

So this is a quick and nasty test.

Password: "iso"

Private Video on Vimeo

So, what I did was set camera to ISO 12,800, aperture to f/16, shutter to 1/50, and I adjusted the light till I thought it was about properly exposed. In hindsight, it's probably better exposed at 8,000 or 10,000 than 12,800, but whatever.

Then I shot at various ISOs up to 12,800.

Then applied curves in post (graded just by eye... and you'll see some differences in the grade).

General point: much better, to my eye anyway, to get proper exposure in camera than in post for event conditions, where you can't control the lights. If I were shooting a short film, I'd try to stick around ISO 640, and adjust lighting to compensate.

Note: I think my results are camera specific (I was using a 5D3 with Lightform picture profile). I'm not sure if the same idea holds for the 5DMk2 or 6D.