Film-Tech Forum ARCHIVE: Running a 500 watt xenon lamp house without the heat filter.

This is topic Running a 500 watt xenon lamp house without the heat filter. in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Alan Gouger (Member # 543) on 06-19-2007, 10:52 AM:

I guess I have a series of questions regarding this topic. I did a search and did some reading which leaves me with the following questions.
I have a ORC lamp house separate PS with a 800 watt bulb soon to drop a 500 watter in her. The lamp house does not have the heat filter.

1. I have read about focus problems and film damage resulting from the UV exposure. At 500/800 watts am I still prone to these issues. The projector is a Devry.

2. If I want to play it safe where would I buy such a filter. I did a google but if someone can recommend a place I prefer it.

3. Could the filter be placed anywhere in the light path before the gate. For instance in the projector after the shutter before the gate or does it have to go in the lamp house. The heat from this lamp house with the 800 watter is almost nothing. The blower fan does a great job. The lamp house nor the projector do not really even get warm to the touch. My previous 1000 watt incandescent bulb heated that thing up so you could not touch it

Thanks for your help!

Posted by Dave Macaulay (Member # 813) on 06-20-2007, 09:39 AM:

The heat filter and a UV filter are different things, although many heat filters have UV absorbing glass and perform both functions. Heat filters reflect infrared energy and pass the visible light at shorter wavelengths, a coating to reflect IR will pass UV. You can make a coating to reflect UV as well, and a multicoated glass plate could do both - but the coating would be more expensive than just using glass that absorbs UV. The energy load of the IR from a xenon bulb would melt anything except fused quartz so the coating is the best approach, but there isn't enough UV energy to make that much heat so absorbing glass is normally used.
If you're not worried about heat - and with a 500W lamp it's not much of an issue I think - you should be able to filter out most of the UV with a fairly cheap UV filtering glass plate. Possibly even a camera type UV filter would survive if the glass is transparent to IR.
If you're using a M1000 lamphouse it really needs some sort of glass plate at the front to get the proper airflow and contain lamp explosions. The usual setup has a flat glass plate or condensing lens at the front and a 2-piece IR reflecting filter in a butterfly wing arrangement just inside the flat plate or lens.

Posted by John Pytlak (Member # 331) on 06-20-2007, 09:59 AM:

Unless your lamp is focused incorrectly to a "hot spot", excessive heating of the film should not be an issue with lamps under 1000 watts. But using a dichroic heat filter is a good idea if your lamp already has one.

Posted by Mark Gulbrandsen (Member # 72) on 06-20-2007, 10:28 AM:

FWIW: The "glass" in the front of that ORC is actually a negative meniscus lens, most of them also had dual heat filters in front of that lens mounted at angles with brass clips. If your lamphouse doesn't have that lens it won't focus properly on a 35mm aperature, you'll have a nasty hot spot. It will work ok on a 16mm aperature though. Even a cracked lens is ok and it can be salvaged by using space shhuttle silicon to glue it back together. Thanks to Strong the heat filters and lens are NLA as far as I know but Optiform has begun producing ORC reflectors again. Roberts Film Service also has a super duper tini reflector that goes into the ORC 1000 and gives more than triple the light output... it is pretty pricey though but quite amazing. With the factory reflector and 500 watt lamp the heat is neglagible but if you really want them they could be custom cut by Ultraflat but it isn't going to be cheap. They are sold by the square inch and since yours have rounded sides you'll also have to pay for that part that is cut off! They make the best heat filters available. I've even installed em in IWERKS 15/70 projectors. Call Bob Destolphi but beware of having your leg talked off [Eek!]

but you'll know alot more about wide screen formats than you do now after he talks to you!!

Mark

Posted by Alan Gouger (Member # 543) on 06-20-2007, 10:50 AM:

Thanks everyone for all this good information. John good to see you posting again and I hope you are having some better days my friend!!

Mark

Thanks for the link for the ultraclear filter. I may be better just buying a new lamp house all together before going that route if its that much.

Also my lamp house has an external PS but I think the rest of it is the same housing as the all in one. Any chance you can still buy parts for these things!

Dave

I was thinking of camera type UV filter. Could it be placed in the projector behind the gate? I do not see an reason this would not work.

[ 06-20-2007, 01:54 PM: Message edited by: Alan Gouger ]

Posted by Dave Macaulay (Member # 813) on 06-21-2007, 01:43 PM:

Camera filters aren't made to take the light intensity (and resulting heat) but will either work or break or melt. Worth a try in my opinion. A larger filter further back towards the lamp will have a lower intensity light flux through a given area and would be less stressed although the physical stress of centre heating might crack them easier. If you have a pro cinema production rental place around they should have large filters for the camera filter boxes, these are at least 6 inches square.

Posted by John Pytlak (Member # 331) on 06-21-2007, 02:11 PM:

You may be able to find suitable IR or UV filters at Edmunds Optics.

Posted by Alan Gouger (Member # 543) on 06-21-2007, 02:36 PM:

John and Dave

This is coming from a novice, I have researched these filters at Edmond's and on line etc. Im confused,some are ether IR or UV. Is these the same, does it matter which I buy just as long as it says it passes visible light?

Thanks again!!

Posted by John Pytlak (Member # 331) on 06-21-2007, 06:55 PM:

When the light goes through the filter, part of the spectrum is removed. A UV filter will remove spectrum below about 400 nanometers. An IR filter will remove spectrum above about 700 nanometers. Filters that remove significant light between 400 and 700 nanometers will change the apparent color of the light.

Posted by Dan Reiter (Member # 1386) on 06-22-2007, 07:11 AM:

A "Hot Mirror", basically the same thing as the filter, can be placed at a 15 degree angle from the light axis up in the nose-cone area, and deflect the heat regions of the light onto a metal surface. If you leave any filter vertical and in the light axis, you have a chance of re-focusing the heat back into the lamp or optics, which could overheat the lamp (BOOM!), or cause other problems. That's how most lamphouse nosecone heat filters work.

I do agree with John, under 1000 Watts, heat is not an issue unless your lamp focus is indeed hot-spotting.