Duh. Just realized the next "real" iso down from 1250 is 640, not 800. But you guys are saying what makes these "real" isos better is noise in highlights, right? Highlights as in what region of the histogram (if you were looking at live view) or what % on a waveform monitor? This noise might not be an issue in a dark night scene.

No.

The noise is ALWAYS going to be in the areas with the least light. That's' why we spend so much time putting light in the shadows. Both on film and in HD. Get that wrong and everything is a muddy mess.

Ah. So if one were planning to work at daringly low light levels for certain scenes, you would recommend lighting "up" then color correcting darker as opposed to just going as dark as you want in cam?

Yep, every time.

Anyone know where this "noise floor" is? I've been attempting to do some informal tests, looking at dark areas in my apartment while looking at the histogram, hooked up to a plasma TV to see the noise. Since it's hard to tell exactly what part of the picture any particular zone of the histogram corresponds to (precisely, anyway), I'm loosely concluding that to be safe, everything should be above 20% (first line of the histogram from the left edge) to be noise free. Sound reasonable?

Sounds about right to me. Not going to look so hot coming off the camera, but it's going to look GREAT in post! And welcome to the reason why when shooting narrative, most experienced people don't worry about "making it look great in the camera". Because unless you are shooting outdoors, or are using a ton of light, it's not going to be clean.

Well, we'll see. The crew may just be me, and I only have so many lights and so much time. I was really hoping to light it as close to the look as possible, and use color correction to polish it, rather than light miles away from the look and use cc to bring it there. It may end up noisy after all.

Well, light it how it's supposed to look, just 3 time as bright! When you bring your levels down in post, it will look just the same. I've attached an example of this from my last film. See the photos for how I shot versus the directors intent.

That is definitely different. Though, to be fair, judging your "bright" still on my unreliable imac monitor, that's still pretty damn dark. Especially in the shadows (near his pants area). I can see noise if I look real hard. I thought you were saying not to really have ANY deep blacks in there while shooting, and to introduce those through color correction. Pants area of the guy and the shadows beneath look pretty damn dark on here.

It was darker than I wanted it to be. But I didn't have full control. Here were my parameters:

1. Warehouse site with no windows, and a translucent ceiling
2. A single 15A plug to accomodate ALL lighting needs
3. A 20ft x 20ft space for the actors to play in
4. We would see about 280 degrees of the set so I couldn't use stands on the set.

I had to light a 20x20 with three practicals.

Welcome to indie cinema!

Let me ask you this, then:

In your original, pre-grade lighting scheme (which is how I planned to light our movie, level-wise, with the intent of probably crushing those blacks later), did you have noise issues? In those dark areas? My original idea with this movie was to light pretty dark for the dark areas, but leave a little information (maybe even more than you did), but getting everything to read, at a minimum, 20% on the histogram would actually be going a lot brighter.

Given the choice, I would have pulled up ALL the blacks you see in this. Yes, there were noise issues, though not bad. I made some tradeoffs between letting it go black or raising ISO. Also, note that this was shot at F4.0 because we only had a lens that would do F3.5 at best. The only thing we had that was faster was a 50mm and it wasn't wide enough.

This is why I STRESS to new filmmakers, BUY GOOD GLASS. I could have saved us from a ton of noise issues in that warehouse if we had some F1.8 or F2.0 glass. But given some of the shots we had to do, I was working at F4 most of the time with only three practicals.

well yes but... F4 is not a bad place to be because you got some DoF to work with rather then against. DoF at 2.0 or less can be pretty thin, and any minor errors that F4 would cover will be obvious at F2 :(. pick your poison.

yes I know, a F2 lens @ 4 will be sharper then a 3.5 or 4 lens wide open.... but since so many folks turn their detail level down, it probably doesn't make much difference. flare level may be another story though.

The poison in this case is noisy footage which will be there even if the focus and acting is perfect. Versus perhaps doing numerous takes to get the focusing right. I'll take my chances on the focus puller versus the noise reduction software! :)

This is a widely held myth. A GOOD F4 piece of glass should be just as sharp. The problem is a lot of F4 lenses are crap. So yea, the faster and more high quality lens will look better stopped down.

I'm afraid the multiples appear to be correct and someone has done the tests to prove it:

http://kriskoster.com/images/5DM2-ISO-Noise.jpg

I've done my own tests as I shoot a lot of night video and the chart appears spot on to me.
I find it fascinating that ISO 640 has the lowest noise and far less noise than ISO 100. My daylight setting is permanently set to 160.