White Limbo Shoot

[mattharding]

Hi,

 

I have a shoot in a few weeks where the director wants to shoot on white limbo. We are shooting super 16 mm with 7217 new film stock. I have used that film stock on a few other shoots and it has been amazing.

 

I spoke with the director and he would like the most brilliant white possible in the background. I would normally take a reflected meter reading and over expose about 2 to 2.5 stops over 18% grey. What is your opinion on how much over 18% grey I should go? At what point will I start seeing noise in the white because of too much over exposure? Is 3 stops too much?

 

What is the perfect number to shoot for?

 

Thanks for your help.

[John Pytlak RIP]

Exposing so the white limbo is 2-3 stops over the whitest white in the scene should be more than enough. Remember, an 18% gray card is 2.5 stops less than a 100% white, so there should be about a 5.5 to 6.5 stop difference between the 18% gray and the limbo white. With too much overexposure, the biggest concern might be flare or "haloing".

[mattharding]

Wow...sorry for dumbing this down so much....but I want to be completely sure I understand what you are saying. Let's say I expose at an f2.8 in order to keep my subject's key light where I want it to be. Then when I take a REFLECTIVE meter reading off the background, my meter should say something like f16? That is a total of 5 stops. 2.5 stops to get me from 18% grey to pure/perfect white and then another 2.5 stops to make it a super brilliant white?

 

Wow, that sounds like a lot. I remember I did something similar before and the white was so overexposed that it got very noisy and grainy. Can the stock handle that?

 

Does all this sound right?

[John Pytlak RIP]

Color negative film certainly has quite a bit of overexposure latitude, such that the limbo white will stay on the "straight line" when you expose the subject normally. As I noted, the first thing you are likely to see with too much exposure is a bit of flaring into the subject.

[mattharding]

Ok thank you John. So at how many stops over the 18% grey reading does the danger of "flaring" begin? 5 stops? 6 stops?

 

Does anyone have any stories, experience, or advise when shooting white limbo practically on a set?

[Michael Nash]

Does anyone have any stories, experience, or advise when shooting white limbo practically on a set?

It's been discussed quite a bit here; check the archives.

 

The fact that you're concerned about noise and grain in the highlights suggest thast you're going to telecine transfer the film to video. Right?

 

You have to remember that in the telecine transfer the contrast is highly adjustable, and yet the filmstock has a sloping curve to its highlight response. In other words, determining a threshold stop for pure white without flaring is a bit of a moving target. But that shouldn't stop you from trying to light and expose for the best results.

 

Mr. Pytlak is correct that 5 or so stops should get you to "peak" white (100 IRE on video). Remember, "normal" white (like a sheet of white typing paper) is about 2.5 stops above middle gray. So if you want bright white, you've got to be even brighter than that. If you're concerned about the film flaring, you'll usually be able to see artifacts like lens flaring on the set by the time you get that bright.

 

But the simplest trick with white limbo is to light a clean white, then do a luminance key in the transfer to key out the white BG. Then you can replace it with a smooth artificial white of any level you choose. If you're afraid of getting a sloppy matte, you can instead crank up the highlight end of the contrast curve with most color correctors and smooth out the white to 90 or 100 IRE. The trick is to light it evenly and smoothly, like you would with green screen.

[oscar jimenez]

just my 10 cents: be careful with that kind of luma keys, I worked with a director once who planned to do stuff with a male model and did a luma key instead of color key, it was difficult to do a key with white because of skin tone. and white was 2.5 stops over key reading

[mattharding]

Thanks --just out of curiosity, is the flairing or haloing caused by one grain being so impacted by the reaction to light that it starts to impact the grain that is next to it?

 

Also, there were a few times where large portions of blue sky filled the frame (shooting 16mm). This was a portion of the sky without the sun in it, yet shooting toward the part of the sky that would not be as impacted by the use of a pola filter. I noticed in the sky a larger amount of graininess. Can anyone explain why?

[John Pytlak RIP]

The halo from a very bright area is usually from lens flare and the beginnings of halation within the film support. Color negative film has rem-jet to help absorb extra light in the film support, minimizing any halation.