Gelling the inside of a light vs. on the doors

[Daniel Wallens]

I have been working sets for a while now (well, I'm still new, but its been about 6 or 7 years), and I still have not heard a real, solid explaination for why it is better to gel a light, be it a fresnel or a kino, on the inside. The only real reason that I've heard which seems logical is that, if you put the diffusion, gel, etc. on the barndoors, then adjusting the barndoors after the light's been gelled becomes a bit harder/more messy. I've heard people try to come up with physics-related and math-related explanations for what the light does when it hits a gel at 3" rather than 5". While this may be true for frames which sit a few feet away, I've never seen any real world difference in light when it hits a subject, depending on whether, say, a 4x4 kino has 1/4 O on the doors, or on the crate or next to the bulbs.

 

Anyone?

[Jonathan Bowerbank]

I think it depends mostly on whether or not you want to melt your gel and possibly damage your light, ha ha

 

I've never put a gel closer to a light more than its barndoors will allow. And really, I see no difference between placing a gel on the barndoors and holding a gel 2 feet from the light on a c-stand. So I don't see what noticeable difference your scenario would conjure.

 

As far as I'm concerned, the inner part of the light is for scrims only, because those usually don't melt.

[David Mullen ASC]

As far as gelling Kinos, I like to place the color gel on the inside and the diffusion around the outside, mainly because you are more likely to be keeping the color gel consistent for the scene coverage... but switching diffusion based on how far or close the light is and how much stop you need from it, plus putting the diffusion around the outside of the doors softens the light more -- diffusion right against the bulbs doesn't really spread the light much more and thus acts more to just lower the output than soften the light.

 

Also, a 4' 4-bank Kino is a pretty big unit and having the color gel wrapped around the outside of the diffusion, with both outside the doors, creates a shinier surface that may cause the kick or bounce reflections onto the set. Plus I can cut the color gel smaller if it's on the inside of the doors.

 

In terms of tungsten and HMI lamps, some of the smaller ones are cool enough to allow the gel to go on the inside of the doors -- probably the gel will fade faster but it can make it easier to work the barndoors.

[Bob Hayes]

I find the best thing to do is wait a day or two and David Mullen will post the perfect explanation of why we do what we do.

[Josh Bass]

I found, while dicking around once, that putting a gel further from a source (I mean like several feet away, on a stand, or something, not a couple inches) increases the saturation of the color, if the subject is at a consistent distance from the light.

[Hal Smith]

I'd put a gel in a frame up against a 1K Tungsten baby and not worry about it. Pars seem to focus infrared just off the lens - best to keep gel away from them. Tungsten seniors and larger eat gel for breakfast - putting the gel out on the barndoors helps to get some cooling airflow to it. Another experience of mine is that deep blues are the first to bleach out, even with modern gels.

[Frank Barrera]

"I found, while dicking around once, that putting a gel further from a source (I mean like several feet away, on a stand, or something, not a couple inches) increases the saturation of the color, if the subject is at a consistent distance from the light."

 

This is interesting. Could you elaborate? ie: How did you measure the "saturation"?

 

Thanks

F

[Chris Keth]

I found, while dicking around once, that putting a gel further from a source (I mean like several feet away, on a stand, or something, not a couple inches) increases the saturation of the color, if the subject is at a consistent distance from the light.

 

I'm pretty sure that it was a psychological thing. I have tested this before out of curiosity and if you measure CTO or CTB with a color temp meter in both situations (I did it with gel on the barndoors, that light being the only one on in the room, then I took the gel off the doors and placed a swatch from the same sheet of gel right in front of the meter sensor and stood in the same place and metered the same way) that you would get the same thing, within the accuracy of the meter and metering technique.

[david freedman]

i thought that puting a gel inside the light (as opposed to the barn doors itself) is to have the ablility to use the barn doors to control the spread/spill....

[Stuart Brereton]

All of my Arri fresnels came with gel frames that fit just in front of the lens, but even the 300w lamps will burn through gel (particularly CTB) if placed there. Gelling the barndoors is fine up to a 2k, but anything bigger, and you should be using a frame.

[Michael Morlan]

Also, a 4' 4-bank Kino is a pretty big unit and having the color gel wrapped around the outside of the diffusion, with both outside the doors, creates a shinier surface that may cause the kick or bounce reflections onto the set. Plus I can cut the color gel smaller if it's on the inside of the doors.

 

One note from Kino Flo. They recommend not clipping gels near the tubes or grid since the lights still need some airflow. You can melt the grid under certain conditions.

[Hal Smith]

All of my Arri fresnels came with gel frames that fit just in front of the lens, but even the 300w lamps will burn through gel (particularly CTB) if placed there.

What brand of gels do you buy? I buy Rosco and don't have much of a problem with it in frames in my 1kW Strand and Colortran babies. I have been known to use Rosco "Heat Shield" behind gels if I think I'm going to put a lot of hours on that particular gel.