Film-Tech Forum ARCHIVE: How do you know if your reflector dichroic coating is gone?

This is topic How do you know if your reflector dichroic coating is gone? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Eric Robinson (Member # 2966) on 04-14-2006, 11:12 AM:

I have several lamphouses (Strong Super Highlight II, with 4000W xenon bulb installed) which seem to generate significant heat despite excellent cooling (bulb, roof exhaust, gate cooling fan.)

I have just installed a new heat filter lens in the snood which is facing the correct way. If I turn the bulb current up to about 90% of the bulbs max rated current, the projection lens becomes very hot ie. you can't touch it with your hand for too long.

The bulb adjustments are set correctly, so that the reflector is not focusing uneeded light on the heat shields or the areas around the aperture.

At this point I'm guessing the dicroic coating of the reflector has died, but I don't know how to test this theory. Any ideas?

Posted by Richard Fowler (Member # 893) on 04-15-2006, 04:00 PM:

The coating is generally golden colored and as it flakes the reflector will throw more I.R. to the film. Flaking and reflector darkening, which causes the most heat, will be at the F1 point of the reflector which is where the arc gap of the xenon bulb is located with in the reflector.
If that is the Strong 15" reflector running 4KW in the Highlight II ( generally )that unit is not as efficient as the newer style 13.5" reflector. Is your dichoric heat filter properly mounted at an angle to reflect the I.R. away from the reflector?

Posted by Jack Ondracek (Member # 1466) on 04-15-2006, 06:50 PM:

Another item that will make a big difference: Make sure your exhaust is drawing more air than the internal blower is pulling. If you can feel heat from your snood, you don't have enough exhaust and the internal blower is pushing hot air into your projector.

My projectors went from hot to nearly cold to the touch when I changed blowers here.

Posted by Monte L Fullmer (Member # 2797) on 04-16-2006, 09:46 PM:

This where the basic question that I have as well - I have X-90's with mirrors that are flaking directly across from the flame point in the bulb.

Course, these mirrors are the mirrors that are doped in the circular frame, thus the mirrors can't act as very good heatsinks due to the isolation of the mirror to frame by the dope.

-Monte

Posted by Gordon McLeod (Member # 33) on 04-17-2006, 10:14 AM:

The heat transfer is from airflow across the back surface of the reflector not the frame

Posted by Cory Isemann (Member # 2517) on 04-17-2006, 11:00 AM:

Say your coating is gone.. can you have it resurfaced? At what cost? Would you save more over time if you just bought new ones?

Posted by Gordon McLeod (Member # 33) on 04-17-2006, 11:01 AM:

UltraFlat will refinish it to a very good efficient hot mirror

Posted by Cory Isemann (Member # 2517) on 04-17-2006, 11:53 AM:

I see they have a product called "UltraClean". Has anyone used this stuff? We have Xetron XCN consoles with 2k bulbs whose reflectors are very hazy. I've tried everything to clean them to no avail. I've just about given up and chalk the appearance of them to age (they're about 11 years old)

Posted by Richard Hamilton (Member # 321) on 04-17-2006, 11:57 AM:

Just dont go beyond the specs of the original blower. I had an interesting conversation with an engineer from Osram. He looked at the design of the Mega lamphouse and told me because of the lamphouse design, we had "cold spots" on the bulb due to the positioning of the fans. He said this would cause some turbulance inside the bulb.

Rick

Posted by Monte L Fullmer (Member # 2797) on 04-17-2006, 12:59 PM:

quote: Gordon McLeod
The heat transfer is from airflow across the back surface of the reflector not the frame

..which is horrible with these early X-90 consoles with that 2 inch blowhole positioned below the cathode seal..since that one blower has to feed both blowholes. Once again..poor lamphouse design...-Monte

Posted by Richard Fowler (Member # 893) on 04-17-2006, 03:15 PM:

Ultraclean has an chalky medium suspended in a liquid with a tiny bit of grit for polishing...guaranteed to destroy any dichoric coating in one polish [Razz]

but fine for rodium or nickel plated reflectors.
I did modifications on a bunch of lamphouses for a manufacturer where the airflow was so imbalanced it was almost a vaccum in the front of the box versus the rear...new air slots in the front made the bulb vendor happy regarding tubulence and explosion issues [Cool]

Posted by Eric Robinson (Member # 2966) on 04-17-2006, 03:19 PM:

quote: Richard Fowler
Is your dichoric heat filter properly mounted at an angle to reflect the I.R. away from the reflector?

Yes, the filter lens is mounted in a metal ring at a slight angle.

I don't have any yellow flaking, just a lot of heat radiation.

I was looking for some type of measurement test method I could employ to test the coating or reflector performance. These reflectors go for $2K to $3K each, so I would hate to recommend a replacement and be out all of that money if I was wrong.

Posted by Mark Gulbrandsen (Member # 72) on 04-17-2006, 08:25 PM:

quote: Cory Isemann
We have Xetron XCN consoles with 2k bulbs whose reflectors are very hazy.

Cory,

You need to get the Big Sky upgrade kits for those consoles. You will get at least double the light out of them with the upgrade. Just did one in Casper, WY last week and light levels jumped way up, especially on the sides.

Typically redone non-dicro mirrors are so close in cost to new factory dicro mirrors that purchasing new mirrors makes far more sense. Keep in mind that you will be getting a standard reflector back... not a dichotic as may have been the original.... then you will need to add heat filters on 3KW and larger lamps so there goes about another 500.00 plus. Re-done mirrors are manily reserved for those with obsolete equipment that cannot obtain any sort of new mirror. Ultraflat can do Dichroic but at great additional cost over the base price of the standard mirror. According to Bob Destolphi at Ultraflat they do very vew of them.

quote: Eric Robinson
These reflectors go for $2K to $3K each

They don't cost any where near that much!

Mark

Posted by Louis Bornwasser (Member # 3063) on 04-17-2006, 08:49 PM:

'bout half of that. Louis