85 filter on an HVX for green screen

Seamus Donahoe · December 16, 2009

Hello,

I've got a bit of a puzzle that I can't quite figure out. I'm currently temping as a manager at Emerson College's student equipment rental facility, and a student has asked to rent an 85 filter for an HVX to be used during a green screen demo. Unfortunately we didn't have one in 82mm, so it was kind of moot anyway, but I'm still curious what it would be for. He said a professor had suggested it, and couldn't give an explanation.

My initial thoughts on this were: well, why would you need a filter when you can white balance to whatever color setting you want (cheeky, I know), but then I thought maybe (under 5600K) greenscreen reflects it's tones more vibrantly thus allowing for the possibility of a more accurate chroma key. This in turn could run the risk of there being too much bounce onto the subjects (space limiting), so the 85 could be called in to cut down on this spill, while maintaining skin tones (if balanced for 3200K).

But then, that means that everything coming in the lens would be balanced, which would equal out the intended effect on the greenscreen.

Either way, I'm stumped. Does anyone have any thoughts on this?

Thanks,

Seamus

Saul Rodgar · December 16, 2009

It does seem odd. Also, the addition of a front of lens filter would also need stop compensation, making it more cumbersome for studio filming than electronic white balance, and I can't imagine anyone setting up green screens outdoors. I prefer blue screen than green screen for chroma key for a number of reasons, but I can't figure why anyone'd want to use the 85 filter with green screen.

Edited December 16, 2009 by Saul Rodgar

Chris Keth · December 16, 2009

I think what he wants to do is cut down on noise in an all tungsten environment. The HVX and a lot of other digital cameras including the RED have chips that are natively balanced to daylight. Balancing them to tungsten can add noise and normally it is negligible but it can mess up a key. HVXs are especially noisy, too, so it would be a definite problem.

Edited December 16, 2009 by Chris Keth

Michael Kubaszak · December 16, 2009

But Chris couldn't you just shoot balanced for daylight(not to mention use HMI's or gel lights or use daylight kino's) and correct it in the edit bay?

Chris Keth · December 16, 2009

But Chris couldn't you just shoot balanced for daylight(not to mention use HMI's or gel lights or use daylight kino's) and correct it in the edit bay?

Yes but that will probably* introduce noise as well since P2 media video is fairly heavily compressed. The video from an HVX isn't particularly high quality and it's quite noisy.

*I've never shot uncorrected greenscreen and corrected it in the edit bay. I have shot other things where it was decided much later to apply a strong color shift and it added a lot of noise that I thought was unacceptable. Unfortunately the production did it anyway.

Chris Keth · December 16, 2009

I should also add that I'm kind of guessing as to the student's reason. Using an 85 on the lens for the noise reason would mean the sensor is natively tungsten balanced, which I doubt it is. Since I have never used an HVX for anything all that serious, I don't know for sure one way or the other.

William Coss · December 17, 2009

It does seem odd. Also, the addition of a front of lens filter would also need stop compensation, making it more cumbersome for studio filming than electronic white balance, and I can't imagine anyone setting up green screens outdoors. I prefer blue screen than green screen for chroma key for a number of reasons, but I can't figure why anyone'd want to use the 85 filter with green screen.

I have actually been on many a day/ext. green and blue screen shots. One that comes to mind was on "The Red Corner". It was over 200 feet long. It was a shame because I really wanted to go to China back then.

Bill

Robert Rock · December 20, 2009

I don't know how or why it actually works, but on the Red, the blue channel is already a little noisy. Balanced under tungsten, it's more so. The 85 actually reduces the noise in the blue channel a lot.

Thing is, for students, tungsten is usually whats around, not to mention cheap compared to most Kino's and HMI's. Adding an 85 to help with tungsten is a much more cost effective fix for those in this type of situation.

Robert Rock · December 20, 2009

It does seem odd. Also, the addition of a front of lens filter would also need stop compensation, making it more cumbersome for studio filming than electronic white balance, and I can't imagine anyone setting up green screens outdoors. I prefer blue screen than green screen for chroma key for a number of reasons, but I can't figure why anyone'd want to use the 85 filter with green screen.

As far as outdoor, a large number of features do this. Peter Jackson had numerous outdoor blue/greenscreen shots in the LOTR films. As far as the blue vs. green debate. most of the compressed formats have much more information in the green channel, which allows for better keys. In uncompressed workflows, blue or green work equally well. It mostly depends on foreground and costumes as to which is better for any given shot.

David Rakoczy · December 20, 2009

Used Green Screen at the Beach, having the Talent run off of it and down the beach... keying/ matte shots are very often shot outdoors.

Saul Rodgar · December 21, 2009

Interesting . . . I don't do a whole lot of chroma key work myself, and only inside, as evidenced by my earlier post. I personally think that outdoor filming with big screens would be too cumbersome. Wind alone would make it far too complicated for the types of productions I am generally part of. As for the green vs blue color of the screen, I have found that I have better luck keying out blue screen than green.

Edited December 21, 2009 by Saul Rodgar

Chris Keth · December 21, 2009

keying/ matte shots are very often shot outdoors.

Not for students, unless they're independently wealthy larvae.

Satsuki Murashige · December 21, 2009

I think what he wants to do is cut down on noise in an all tungsten environment.

If the guy was using a blue 80 series filter, then this would make sense. But why use an amber 85? It will just make your tungsten lights MORE orange! I used to work on low-budget corporates where we shot daylight or tungsten green screen on the HVX/HPX500/EX1/EX3 depending on whether the room had windows or not. Never once used an 85, just white-balanced the camera. They kept hiring us, so I guess it wasn't a problem...

Green provides a better key for most video formats, but it spills more because it's brighter and thus more reflective. So for a small confined space, blue may be a better choice. I've worked on a ton of chroma key video shoots, and it's almost always green. The one time we used blue was when the talent's costume had green in it (it was a giant, dancing foam corn-on-the-cob!). I don't know which is better for film - I recall hearing that the blue layer is more sensitive than the green. If that's true, then the blue would probably key better.

It doesn't have to be expensive to do green screen outside - you may only need a small bit of green depending on what you're trying to key. Check this out: http://videocopilot.net/tutorial/advanced_car_hit/.

David Rakoczy · December 21, 2009

It doesn't have to be expensive to do green screen outside - you may only need a small bit of green depending on what you're trying to key. Check this out: http://videocopilot.net/tutorial/advanced_car_hit/.

Exactly... you can do Green/ Blue Screen with a 6x6.. 4x4... 2x2... or paint a wall... piece of wood.... (I carry a 12x12 and a 6x6).

Chris Keth · December 21, 2009

If the guy was using a blue 80 series filter, then this would make sense. But why use an amber 85? It will just make your tungsten lights MORE orange!

I was meaning this concept but opposite: a tungsten camera in daylight. I'm not sure this exists, though. All of the sensors seem to be daylight native.