Film-Tech Forum ARCHIVE: Judging reflector quality

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Posted by Michael Schaffer (Member # 1204) on 04-20-2007, 07:17 PM:

What's the best way to judge the state of quality an older reflector is in visually? A lot of reflectors which have been in use a umber of years have quite a bit of dust on them as theater people rarely seem to clean them when changing the lamp.

Often, when you clean them off carefully with a soft cloth, you get rid of most of that but find a layer of dust has been baked into the reflector. Obviously, there is no way to get that off without damaging the reflective coating itself. Sometimes you find they did actually clean the reflector, and then you often have smears from lens cleaner or whatever was used and scratches. I don't really see a point in cleaning a reflector with anything but a soft cloth anyway. Typically, there are no (or shouldn't be at leasy) any smears or fingerprints on them as you often find on lenses, or other exposed optical surfaces such as sound optics which often have some goo from oil and film shedding on them.

And then of course the coating gets hazy over the years, especially when the lamphouse is too hot.

When you look at the reflector, how do you look at it to establish in what state it is? They do look very different depending on from what angle and distance you look at them, and what color and quality your light source has. I usually look at the surface from a close distance to see if there is any dust baked into it, and that is of course easy to see. But the overall reflective or "shine" of the reflector isn't easy to judge. Do you have any "tricks" for that?

BTW, what were the recommended and maximum operating temperatures for xenon lamps again? I mean the temperature of the metal end pieces just after the lamp hase been switched off. I had those figures noted down somewhere, but can't find the file right now.

Posted by Monte L Fullmer (Member # 2797) on 04-20-2007, 10:14 PM:

...going back to my glass reflector/carbon arc days - we would make a paste of this scrubbing cleanser of "Bon Ami." This paste compound would scrub off the haze from the the surface of the mirror of carbon soot and dust, yet never scratched the mirror(s) surfaces itself.

Posted by John Hawkinson (Member # 1135) on 04-20-2007, 11:32 PM:

Osram says the base temperature must not exceed 230 degC (446 degF).

As for reflectors, I don't know, but I'd speculate the best test is to measure the light output against a known value. This doesn't account for lamp variation, though...

--jhawk

Posted by Jack Ondracek (Member # 1466) on 04-21-2007, 01:06 AM:

quote: Monte L Fullmer
...going back to my glass reflector/carbon arc days - we would make a paste of this scrubbing cleanser of "Bon Ami."

That was great stuff for the back-coated reflectors we used in the arc days, but probably not something you'd want to use on a front-coated reflector... unless, of course, you wanted to take that nasty front coating clean off. It'd probably work fine for that! [Eek!]

Posted by Mark Gulbrandsen (Member # 72) on 04-21-2007, 08:29 AM:

You should really call and talk to the guys at Optiform. In 10 minutes you will know more about reflectors than you want to....

Mark

Posted by Gordon McLeod (Member # 33) on 04-21-2007, 11:49 AM:

UltraFlat makes an excellent cleaner for reflectors

Posted by Ken Lackner (Member # 1002) on 04-21-2007, 01:06 PM:

quote: Mark Gulbrandsen
You should really call and talk to the guys at Optiform. In 10 minutes you will know more about reflectors than you want to....

I had similar concerns, and I called Optiforms last week. They weren't much help, and basically said that it would be better for me to talk to the OEM's (Strong, Neumade, etc...).

Agreed with Gordon on UltraFlat's cleaner, called UltraClean. It's about $25 a bottle, but you only need a little tiny bit and in many cases it can clean a reflector that may seem otherwise uncleanable.

Posted by Mark Gulbrandsen (Member # 72) on 04-21-2007, 05:55 PM:

Am surprised you didn't get any useful info from Optiforms. I net theiir President at Showorst a few years ago.... He is a U of I grad and he and I talked for about an hour about relectors and optics, in fact we went over and looked at Roberts Film Service reflector together and he told me he could easily make that reflector out of metal.

Mark

Posted by Michael Schaffer (Member # 1204) on 04-21-2007, 08:24 PM:

Why don't you share some of the wisdom you gained from that with us? How do you visually judge reflector quality?

Posted by Frank Angel (Member # 248) on 04-22-2007, 04:25 PM:

Or at least the telephone number.

Where do you buy Ultraclean?

Contact info for Optiform?

Thanks

Posted by Ken Lackner (Member # 1002) on 04-22-2007, 04:57 PM:

www.optiforms.com

UltraClean can be purchased from UltraFlat. www.ultraflat.com

Posted by Mark Gulbrandsen (Member # 72) on 04-22-2007, 10:04 PM:

quote: Michael Schaffer
Why don't you share some of the wisdom you gained from that with us?

I learned more about how reflectors are actually made and what types are possible to make from electroform. A reflector that is cloudy is that way because the metal coating is oxidized and has turned white.... a normal thing for all unprotected aluminum and rhodium surfaces to do. In fact the self oxidation of aluminum is a good thing because the oxide coating actually protects the aluminum from further deterioration, like self preservation. In reflectors this oxidation is a bad thing as it cuts the efficiency of a reflector way down. Considering that the dicro coating is but a few molecules thick at best the metalized surface especially if its exposed to harsh atmospheric conditions such as the air here in SLC or the air in L.A. will still eventually oxidize. In this case the cleaners from Ultraflat still won't work to clean it up unless the dicro coating is first completely removed. Straight metalized reflectors like in old ORC, Xetron and other old lamp houses can SOMETIMES be polished gently with the Ultraflat polish with good results obtained. I recently tried this stuff on an Eprad mirror up in Powell Wyoming and it really didn't do much.... the mirror was way to oxidized and a more abrasive polish would first be needed just to break through the oxide layer.

I threw this together in a few min and I'm sure I'm not 100% correct but the basics are there... hope this helps some... Anyone else want to have a go at it be my guest. Another good person to talk to is Bob Destolphi at Ultraflat.. [thumbsup]

. Bob's a very knowledgable guy.

Mark

Posted by Ken Lackner (Member # 1002) on 04-22-2007, 10:54 PM:

Yes, Bob is the man. He can most certainly tell you more than you will ever want to know about reflectors. That's where I learned most of what I know about the subject.

Good info there, Mark. I have some discolored non-dichroic ORC reflectors that I will be replacing soon. Just for giggles, I'll try polishing one of them with UltraClean after I remove it from service just to see what kind of results I can get. By the way, what causes that rainbow coloring on a non-dichroic?