Film-Tech Forum ARCHIVE: Max gate temperature

This is topic Max gate temperature in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Antonio Marcheselli (Member # 373) on 08-22-2004, 05:44 PM:

Hi everyone

How is the maximum temperature that can be reached on a gate? It depends of the lamp, of course. I have 2500, 4000 and 7000W on Cinemeccanica V5

Bye
A

Posted by Frank Angel (Member # 248) on 08-22-2004, 06:06 PM:

Antonio, I asked that very question awhile back (can't find it with Search) but we wound up discussing how to tell when the radiant energy to the film is too much by what it does to the film (embossing the emulsion, the beginnings of blistering, etc.), but we didn't come up with a definitive answer as to exactly what was safe, like such-and-such a release print film cannot tolerate a mean temperature of such-and-such degrees f. or c. I found that strange, given that every other parameter of 35mm film is so minutely specified. One would think that a maximum temperature tolerance figure would be part of the specs of every type of print film. If we knew that max figure, a heat probe meter could easily be stuck in the aperture and a direct reading could be obtained. You would then know how close to the maximum temperature your optical system is pumping radiant energy.

Naturally various film stocks will have different tolerances, but if you set your system to the film stock that has the lowest maximum temperature tolerance (say a black and white, high silver content acetate print), then you would be confident that your system was safe for all print types.

But then, I am not the CEO of Eastman Kodak. [Wink]

Posted by Antonio Marcheselli (Member # 373) on 08-22-2004, 06:32 PM:

I made a search too and I found nothing.

Perhaps you're right, a probe would be the best solution.

Bye
A

Posted by John Pytlak (Member # 331) on 08-22-2004, 08:29 PM:

Heat Damage:

Heat Damage 1 pdf

Heat Damage 2 pdf

Kodak's Paul Preo wrote an excellent paper about the effects of radiant energy on prints:

Preo, Paul H., Projection Performance of Theatrical
Motion-Picture Films Using Xenon
Short-Arc Lamps, 92:938, Sept. 1983 SMPTE Journal

Thermal damage to color print film starts when the temperature of the emulsion reaches about 200 Celsius.

A "heat probe" or themocouple really doesn't tell the real story, as the exposure time of a print frame is normally only for two 1/96 second "bursts" of energy. A thermometer in the gate will see the cumulative effect of the radiant energy, reaching a very high temperature.

[ 08-24-2004, 09:22 AM: Message edited by: John Pytlak ]

Posted by Antonio Marcheselli (Member # 373) on 08-23-2004, 05:07 PM:

Thank you John

I mean the temperature of the iron skates, where the print is touching while it's projecting.

Bye
A

Posted by John Pytlak (Member # 331) on 08-23-2004, 10:14 PM:

Try to keep the gate as cool as possible (that's what water cooling is for), but the film will normally survive up to 200 Celsius while the projector is running, even if your fingers get burned.

Posted by Antonio Marcheselli (Member # 373) on 08-24-2004, 07:30 AM:

Thank you John, for the F/C conversion too!!

I was asking this because I was thinking what kind of lubricant can I put in the gate's area without having it cristallizing.

I have silicon grease that is stable up to +230°C.

I'm not putting grease on the gate, don't worry!

Bye
A

Posted by John Pytlak (Member # 331) on 08-24-2004, 09:21 AM:

Keeping the gate free of burrs, nicks, and hardened gelatin deposits is probably all you really need to do. I find a fingernail, hardwood "orange stick", or plastic guitar pick is normally enough to remove hard deposits, followed by a stiff bristled tooth brush. Definitely avoid metal tools which may nick or gouge the film-contacting gate runners.

If the prints are properly lubricated/treated, there should be no need to lubricate the runners. I have seen some projectionists use a hard wax like carnauba to lubricate the gate after cleaning. Others might use a bit of FilmGuard, XeKote, or other lubricating film treatment on the gate runners, but film lubricant is most effective when used on the print, since any lube on the gate is quickly worn away.

Posted by Antonio Marcheselli (Member # 373) on 08-24-2004, 10:15 AM:

I completely agree with you John, I don't want to put anything on the gate. Just on the aperture plates's rail that are very near the gate!

The gates, and the print, will stay as clean as possibile and free of any type of lubricant, be sure!!

Bye
A

Posted by Peter John Anthony. C (Member # 2500) on 08-24-2004, 10:44 AM:

[Try to keep the gate as cool as possible (that's what water cooling is for), but the film will normally survive up to 200 Celsius while the projector is running, even if your fingers get burne]

Film survives up to 200 Celsius, can you let me know about the lens as well.
Thanks.

Posted by John Pytlak (Member # 331) on 08-24-2004, 08:41 PM:

quote: Peter John Anthony. C
Film survives up to 200 Celsius, can you let me know about the lens as well.
Thanks.

Fortunately, the film absorbs much of the radiant energy, so the lens is saved from too much heat. That's why you need to be careful to limit the time you project "open gate" for screen luminance measurements, lest you damage the lens.