Film-Tech Forum ARCHIVE: Glass- or metal-mirror, wich is best?

This is topic Glass- or metal-mirror, wich is best? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Thomas Jonsson (Member # 1902) on 06-03-2005, 03:07 PM:

When it comes to cold light mirrors, would you say a glass
mirror performs better than a metal mirror? The latter is
less expensive, but does it mean the quality is equally lower?

I use Cinemeccanica Zenith X4000H lamphouses, and as far as I
know glass mirrors are not available - not in Sweden, anyway, so
I haven´t been able to compare.

Thomas

Posted by John Pytlak (Member # 331) on 06-03-2005, 03:17 PM:

The lamphouse needs to be specifically designed to use a "glass" mirror, as the infrared energy goes through the mirror, so there should be a heat sink or heat deflector behind it to protect any components. With a metal mirror having a dichroic coating, the metal of the mirror IS the heat sink, and needs to have good airflow to keep it cool and maintain its efficiency in getting rid of the heat.

I've always felt glass mirrors were theoretically likely to have better efficiency, as you did not have the issue of all the IR being trapped by the mirror itself. But it really depends on the design of the lamphouse and efficiency of the dichroic coatings.

Posted by Steve Guttag (Member # 268) on 06-03-2005, 04:04 PM:

Glass definately gives you less heat per watt on the film itself. Glass also tends to be a more uniform reflector. However, the reflector's design is key to getting the best light out of the lamphouse/console. We have had excellent results from both metal and glass...I'm partial to the glass ones though.

Posted by Richard Fowler (Member # 893) on 06-03-2005, 06:41 PM:

My personal preference is glass in a well maintained system and trained personel and metal for all popcorn operators [Big Grin]

USA is metal centric and the majority of the world, glass lovers [Razz]

Glass vendor quality can be an issue; I have seen some dichoric glass units looking great after three years @ 10 hours a day to coatings flying off the glass at 500 hours.

Posted by Louis Bornwasser (Member # 3063) on 06-03-2005, 08:09 PM:

If you think about it, we had 11,000+ watts in the Super Corelite and heat was not a problem. A metal reflector in this lamphouse would have been an impossibility.

Glass reflectors were cheap to make once the production equipment was purchased. The hard part was the front coating. At Strong/Toledo this was a low tech operation.

What doomed the glass reflectors was then then-current "deep dish" reflectors. Now that we are back to a more moderate curve, it would seem that we now lack production facilities that do not cost an arm & a leg!

Louis

Posted by Mark Gulbrandsen (Member # 72) on 06-03-2005, 08:56 PM:

quote:
What doomed the glass reflectors was then then-current "deep dish" reflectors. Now that we are back to a more moderate curve, it would seem that we now lack production facilities that do not cost an arm & a leg!

Well, there is one major west coast metal mirror manufacturer that supplies just about everyone in the States. They claim that they can design metal mirrors today that can perform exactly the same same as any given glass mirror...... so I was told by their president and chief designer......... I don't quite agree though.

Mark

Posted by Steve Guttag (Member # 268) on 06-03-2005, 11:09 PM:

Use Kinoton's "light projector" on a glass reflector and on a metal one....you will see just how ununiform Optiform (USA metal reflector manufacturer) reflectors can be. However, I've found that Optiform's reflectors are much more consistant than reflectors used to be in the 80s. Even using the old string method will show off the lack of uniformity (the reflected line has waves).

Posted by John Walsh (Member # 168) on 06-04-2005, 09:29 AM:

Glass is better, but when a bulb explodes it's 'game over.' In the USA, theaters leave bulbs in well after the warrenty has expired. This means the bulb manufacturer won't pay to replace a reflector if the bulb explodes.

But the image with glass can be really nice. It's not just better light; the focus improves too.

Posted by Louis Bornwasser (Member # 3063) on 06-04-2005, 09:19 PM:

"Game Over" for bulb explosions in glass reflectors is exactly what we want! This guarantees excellence. Also, the technology involved SHOULD be less expensive for the glass....like it once was.

Louis

Posted by Michael Schaffer (Member # 1204) on 06-05-2005, 04:30 AM:

It's pretty much "game over" when an explosion occurs in a lamphouse with metal reflector too. Yes, you can still play, but the reflector is usally dented so badly you have to change it anyway because the image becomes too dark and too unevenly lit.

Posted by Sam D. Chavez (Member # 1841) on 06-05-2005, 11:00 AM:

Michael,

You are being charmingly logical and naive, but as long as any light leaves the lamphouse, management won't pay for a change of the reflector.

Also there are a large number of lazy technicians.

Posted by Louis Bornwasser (Member # 3063) on 06-05-2005, 12:09 PM:

Time here for an Amen, Amen! to Sam's reply.

Posted by Michael Schaffer (Member # 1204) on 06-05-2005, 04:08 PM:

Not necessarily. I did in fact find some dented or peeled reflectors in our older projectors which had apparently been in there for a long time, and I was able to replace them without much discussion after I demoed the before/after effect.
In our new location we put in all complete Kinoton packages including the lamphouse/console with glass reflector, and while I made our owners aware of the "risk factor" of the glass reflectors, they were hit by the image quality, the brightnesss and evenness of illumination (plus stability and quietness, but that is of course an entriely different subject) like with a hammer and are now big fans of the concept.