Premium Member Phil Rhodes Posted August 6, 2015 Premium Member Share Posted August 6, 2015 Two bits of Lee 203 have a mired shift of -35 each, for a total of -70. One bit of Lee 202 has a mired shift of -78. Um. P Link to comment Share on other sites More sharing options...
Premium Member Adrian Sierkowski Posted August 6, 2015 Premium Member Share Posted August 6, 2015 This is common knowledge that two quarters don't make a half, just as two halves don't make a full. I suspect it has to do with; well physics (moreso the thickness of the gel; the air-gap between two gels, a slight color compounding in the underlying medium to which the gel pigmentation is applied, and general goblins. ) Though in truth; often, though not perfect, douvbling halves or quarters or eights etc is as they say "good enough for government work" Link to comment Share on other sites More sharing options...
Premium Member David Mullen ASC Posted August 6, 2015 Premium Member Share Posted August 6, 2015 I agree that it's not exact, the MIRED shift isn't even consistent across manufacturers for standard color correction gels. The question is how often it's a problem. Link to comment Share on other sites More sharing options...
JD Hartman Posted August 6, 2015 Share Posted August 6, 2015 Speaking of "air gap", is is better to have the two sheets touching or spaced apart? I've had DPs insist on spacing the two sheets applied to opposite side of an open frame with some wadded gaff. Any science between one method or the other? Link to comment Share on other sites More sharing options...
Premium Member David Mullen ASC Posted August 6, 2015 Premium Member Share Posted August 6, 2015 Not sure why that would matter. Link to comment Share on other sites More sharing options...
Robin R Probyn Posted August 7, 2015 Share Posted August 7, 2015 Building up the overtime.. ? Link to comment Share on other sites More sharing options...
JD Hartman Posted August 7, 2015 Share Posted August 7, 2015 Building up the overtime.. ? That would only make sense on a union shoot. Anyway....I think I going to shoot an an email to Rosco. Would be good to be able to get a definitive answer on "air gap", if one exists. It will probably fall into the Double Jeopardy category: "Misconceptions in the Grip department". Link to comment Share on other sites More sharing options...
Robin R Probyn Posted August 7, 2015 Share Posted August 7, 2015 worried about the heat welding them together.. only thing I can think of.. Link to comment Share on other sites More sharing options...
Premium Member Phil Rhodes Posted August 7, 2015 Author Premium Member Share Posted August 7, 2015 I was gonna say, cooling. Link to comment Share on other sites More sharing options...
Premium Member Aapo Lettinen Posted August 7, 2015 Premium Member Share Posted August 7, 2015 Speaking of "air gap", is is better to have the two sheets touching or spaced apart? I've had DPs insist on spacing the two sheets applied to opposite side of an open frame with some wadded gaff. Any science between one method or the other? probably for cooling. if you have dense gels they would build up lots of heat and the one closer to the lens may melt at least a bit Link to comment Share on other sites More sharing options...
Premium Member David Mullen ASC Posted August 7, 2015 Premium Member Share Posted August 7, 2015 Yes, and maybe it also slows down the fading from heat. Link to comment Share on other sites More sharing options...
Sanjay Sami Posted August 7, 2015 Share Posted August 7, 2015 JD, would love to know what Rosco or Lee have to say. Ive always stuck them together. Maybe its time to change :-) Link to comment Share on other sites More sharing options...
Premium Member Aapo Lettinen Posted August 7, 2015 Premium Member Share Posted August 7, 2015 it depends a lot on what gels you use. for example CTB heats a LOT more than a CTO (you can see this by comparing the transmission percentage. if a gel has for example 25% transmission then you can assume that about 75% of the visible light hitting the gel converts to heat (maybe less because the gel surface also reflects small amount of the light back to the fixture) . and that is A LOT of heat if you are using for example 5K tungsten behind a CTB Link to comment Share on other sites More sharing options...
JD Hartman Posted August 8, 2015 Share Posted August 8, 2015 Rosco said: In general, if you place two filters in a frame together so that they are touching, they will eventually melt together. So, although I don’t specifically know, my guess is that yes what you are describing is an in the field solution to keep the filters from melting together. That will help them remain usable longer. Hope that helps! Wendy Wendy Luedtke Product Manager for Color and Lighting Rosco Labs Link to comment Share on other sites More sharing options...
Robin R Probyn Posted August 8, 2015 Share Posted August 8, 2015 thanks for the up date.. Link to comment Share on other sites More sharing options...
Sanjay Sami Posted August 8, 2015 Share Posted August 8, 2015 Thanks JD Link to comment Share on other sites More sharing options...
JD Hartman Posted August 8, 2015 Share Posted August 8, 2015 (edited) I'm hoping that she will forward the question on at Rosco Labs and I'll be able to share a more scientific answer. The heat dissipation thing does make sense, now we need empty flat frames with heat dissipation channels so we can have convective cooling of the gels. Edited August 8, 2015 by JD Hartman Link to comment Share on other sites More sharing options...
Sanjay Sami Posted August 9, 2015 Share Posted August 9, 2015 Ha ha ha :-) Ive honestly never had gels melt together in a situation that would not have melted a single one. However, if it helps maintain the colour for run of show I wouldn't mind trying that. Link to comment Share on other sites More sharing options...
Brian Drysdale Posted August 9, 2015 Share Posted August 9, 2015 I suspect the colour will fade or discolour before the gels actually melt together. Link to comment Share on other sites More sharing options...
Premium Member Phil Rhodes Posted August 9, 2015 Author Premium Member Share Posted August 9, 2015 I have these PARs which are extremely efficient but create a very high intensity beam. They melt gels like an industrial cutting laser, and I'm only exaggerating slightly. Link to comment Share on other sites More sharing options...
Sanjay Sami Posted August 10, 2015 Share Posted August 10, 2015 Phil - use heat shield to protect your gels. Link to comment Share on other sites More sharing options...
Premium Member Phil Rhodes Posted August 10, 2015 Author Premium Member Share Posted August 10, 2015 Good thought. Interestingly, the Rosco site does suggest a one-inch air gap between the heat shield and any other filters, for the reasons of cooling we've been discussing. I shall leech an image from their server to illustrate: Link to comment Share on other sites More sharing options...
Sanjay Sami Posted August 13, 2015 Share Posted August 13, 2015 Yes, I would use more than and inch. Probably more like 6 to 8 inches between heat shield and coloured gel. Link to comment Share on other sites More sharing options...
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