500T and Green Screen Qs

[David Szasz]

Hi All,

I'm shooting a music video in a week's time and am wondering if anyone has had any experience shooting green screen work on 500T/7219? 

I shot some tests on 250D and was able to pull a key successfully but we will now potentially be shooting some scenes on 500T and am wondering if this is still ok for keying?

My thinking is to rate the stock at 320ASA and use tungsten balanced lights to illuminate the green screen to one stop under key. The subject needs to be overexposed for story reasons (she's glowing and floating in the final comp). I was thinking around 2 to 3 stops over would be enough to work with in the grade without blowing things out too much. If my iris is set to T4 and the subject reads around T9, will I still be ok to light the screen to T2.8? Is it safer to light it to a T4 because I'm intentionally overexposing the subject. And, how would this overexposure effect the key in terms of halation and sharpness?

I should really do another test but I don't think time will allow it. Any thoughts or advice from those more experienced than me would be greatly appreciated.

Thank you 🙂

[Tyler Purcell]

It's about separating your action/subject from the background, if there can be good definition, you should be ok. The moment you have some reflection of the green on your action/subject, then you're going to be lost. 

[M Joel W]

That all sounds about right to me. I would avoid diffusion filters, etc., but I doubt film halation will present issues that can't be tackled in post. 

Far more often I see overexposed rather than underexposed green screens. So that sounds right. I forget exactly but believe the conventional wisdom is to expose a green screen a stop under 18% gray through the spot meter rather than the incident meter, and this correlates with exposing at key (not a stop under) with the incident meter roughly? Correct me if I'm wrong; I likely am. If you are going to use a really bright background (like a bright sky or something; anything brighter than the subject) I think you can expose the green screen brighter and it will actually help in comp as the matte lines will start brighter and integrate better. 

You can get away with a lot using denoising software (Neat Video). I think rating at 320 ISO is not a bad idea but the grain structure should be manageable with some software. 

[David Szasz]

22 minutes ago, M Joel W said:

That all sounds about right to me. I would avoid diffusion filters, etc., but I doubt film halation will present issues that can't be tackled in post. 

Far more often I see overexposed rather than underexposed green screens. So that sounds right. I forget exactly but believe the conventional wisdom is to expose a green screen a stop under 18% gray through the spot meter rather than the incident meter, and this correlates with exposing at key (not a stop under) with the incident meter roughly? Correct me if I'm wrong; I likely am. If you are going to use a really bright background (like a bright sky or something; anything brighter than the subject) I think you can expose the green screen brighter and it will actually help in comp as the matte lines will start brighter and integrate better. 

You can get away with a lot using denoising software (Neat Video). I think rating at 320 ISO is not a bad idea but the grain structure should be manageable with some software. 

Thank you Joel, that's great insight. Great point about exposing the screen brighter for bright backgrounds, haven't thought about that before. Regarding spot metering, I share the same understanding.