camera's exposure meter for greenscreen? at DVinfo.net

Josh Bass · June 13th, 2006, 02:26 PM

I'm DPing a no-budget short soon, and we're talking about doing one little bit against a greenscreen--a locked off shot of a talking puppet, with background to be inserted later.

So, I don't have light meter (well, I do, but it's $60 and I wouldn't trust it much for exposure-critical work), nor a waveform monitor. I was wondering, though, if the XL1s/XL2's "exposure meter" (the little sliding meter thing in the upper left part of the viewfinder) would be a way to check the evenness of the lighting on a green screen. What I'm thinking of is just zooming in on different portions of the screen to make sure they're all at the same fstop (since you can't really tell by eye), kind of like spot metering it with the camera. Will this work? Is it accurate enough? We don't have to do the greenscreen thing at all, and I'd rather not do it than screw it up.

Marcus Marchesseault · June 13th, 2006, 04:28 PM

You could use the zebra bars on your camera. Light the screen and look at it throught the viewfinder with zebra bars on. Adjust the exposure until you are right on the edge of getting zebra bars and you will see which areas are over and under lit. Try setting the bars at both 70 and 100 ire to see if that gives you a better idea.

Josh Bass · June 13th, 2006, 04:49 PM

I see how that could work, but I was wondering more about the actual exposure meter being used to judge the levels.

Also does anyone know how the notches on the meter correspond to stops? I mean, does one notch to the left of ideal exposure = 1 stop under, etc.? How precise is it? Half stops? 3rds?

How many stops under should the screen be relative to what the iris is set at?

What's the tolerance for greenscreen keying? How different can the levels be on different areas of the greenscreen before it won't key correctly any more? This would be using an XL2/XL1s to shoot, and Vegas for the post/keying.

Dean Sensui · June 14th, 2006, 12:03 AM

Josh...

As Marcus mentioned, the zebras will give you the best info on exposure. Zebras will give you signal level, and that's a very important part of doing green screen work, along with chroma levels and purity.

Also, if you need a very even green screen, zebras will tell you where the bad spots are.

Give it a test and see.

For some good green screen info and tips, check this out:

http://www.imageshoppe.com/HVX_bluescreen2.html

For something really impressive, take a look at this:

http://www.studiodaily.com/main/tech...dies/6503.html

June 13th, 2006, 02:26 PM	#1
Josh Bass Slash Rules! Join Date: Apr 2002 Location: Houston, Texas Posts: 5,472	camera's exposure meter for greenscreen? I'm DPing a no-budget short soon, and we're talking about doing one little bit against a greenscreen--a locked off shot of a talking puppet, with background to be inserted later. So, I don't have light meter (well, I do, but it's $60 and I wouldn't trust it much for exposure-critical work), nor a waveform monitor. I was wondering, though, if the XL1s/XL2's "exposure meter" (the little sliding meter thing in the upper left part of the viewfinder) would be a way to check the evenness of the lighting on a green screen. What I'm thinking of is just zooming in on different portions of the screen to make sure they're all at the same fstop (since you can't really tell by eye), kind of like spot metering it with the camera. Will this work? Is it accurate enough? We don't have to do the greenscreen thing at all, and I'd rather not do it than screw it up. __________________ The Bass' camerawork The Bass on IMDB

June 13th, 2006, 04:49 PM	#3
Josh Bass Slash Rules! Join Date: Apr 2002 Location: Houston, Texas Posts: 5,472	I see how that could work, but I was wondering more about the actual exposure meter being used to judge the levels. Also does anyone know how the notches on the meter correspond to stops? I mean, does one notch to the left of ideal exposure = 1 stop under, etc.? How precise is it? Half stops? 3rds? How many stops under should the screen be relative to what the iris is set at? What's the tolerance for greenscreen keying? How different can the levels be on different areas of the greenscreen before it won't key correctly any more? This would be using an XL2/XL1s to shoot, and Vegas for the post/keying. __________________ The Bass' camerawork The Bass on IMDB

June 14th, 2006, 12:03 AM	#4
Dean Sensui Inner Circle Join Date: Oct 2001 Location: Honolulu, HI Posts: 2,054	Josh... As Marcus mentioned, the zebras will give you the best info on exposure. Zebras will give you signal level, and that's a very important part of doing green screen work, along with chroma levels and purity. Also, if you need a very even green screen, zebras will tell you where the bad spots are. Give it a test and see. For some good green screen info and tips, check this out: http://www.imageshoppe.com/HVX_bluescreen2.html For something really impressive, take a look at this: http://www.studiodaily.com/main/tech...dies/6503.html __________________ Dean Sensui Exec Producer, Hawaii Goes Fishing

June 13th, 2006, 04:28 PM	#2
Marcus Marchesseault Trustee Join Date: Nov 2005 Location: Honolulu, HI Posts: 1,961	You could use the zebra bars on your camera. Light the screen and look at it throught the viewfinder with zebra bars on. Adjust the exposure until you are right on the edge of getting zebra bars and you will see which areas are over and under lit. Try setting the bars at both 70 and 100 ire to see if that gives you a better idea.