Film-Tech Forum ARCHIVE: Fairly cheap double coated glass for port windows.

This is topic Fairly cheap double coated glass for port windows. in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Frank Angel (Member # 248) on 06-18-2005, 01:34 AM:

Edmund Scientific:

Tech Spec High Efficiency Anti-Reflection Coated Windows.
- Yield Ultra High Transmission
- Eliminate Back Reflections

The these glass windows are coated on both sides with Clear Display Anti-Reflection Coating (CDAR) reducing reflectance to less than .05%. Back reflections are virtually eliminated by the coating, so these windows offer improved readability when used in industrial displays or computer monitors. Their high transmission makes them ideal for many other optical applications.

It goes on further to say the transmission is between 96-99% and the coating is multi-layered AR on both sides. They are sold in various sizes up to 10"x12", but oddly enough, they don't give the thickness. The 8x10" piece is $36.30, which is a heck of a lot cheaper than what I found from a cinema supply house.

Sounds like the right stuff to me.

They also make "Clear Optical Cast Plastic" windows for those who are used to using Lexan, like me. The difference being that they claim New plastics technology has produced windows compared to similar available transparant plastics, Thermoset ADC windows have the highest transmission and lowest haze, have at lease 20-25 times greater abrasion resistance.

8"x10" (comes no larger) goes for $38.90 Sounds like it is better than the Lexan I used in on theatre, but I would opt for the coated glass instead at even less cost.

Edmund Industrial Optics - 800-363.1992 and www.EdmundOptics.com

Posted by Mark Gulbrandsen (Member # 72) on 06-18-2005, 10:10 AM:

Frank,

You can also look for those Xerox machine glass windows. Those are also usually coated glass and available at surplus places.

Mark

Posted by John Pytlak (Member # 331) on 06-20-2005, 08:26 AM:

8x10 inches is quite small, and may not be sufficent for short throw applications (shorter focal length lenses). You do want some clearance in front of the projector.

LEXAN and other plastics often "light pipe", with internal reflections causing flare. Optical quality glass with anti-reflection coatings is best:

Conquering Contrast Killers

quote:
Contrast Killer 5: Poor Ports
The projection port is just as important as the lens in delivering high-quality
images. Plain window glass should not be used. Only optical quality glass with
anti-reflection coatings should be used. Port glass should never be installed
perpendicular to the projection beam, to avoid reflecting light back into the
projector lens. Likewise, if two panes of port glass are needed for sound
isolation, care should be taken to avoid internal re-reflection. Soundproof,
angled port glass frames are available from several vendors. Port glass should
be absolutely clean and scratch-free. As with the projection lenses, loose dust
should be gently brushed away with a camels-hair lens brush, and liquid lens
cleaner and lens tissue used for cleaning any haze. Ideally, the projected
image should be almost invisible on the port glass, with no detectable
scratches or haze.

Posted by Larry Myers (Member # 738) on 06-20-2005, 07:47 PM:

A good test. If you can clearly see an "out of focus" image on the glass as the projector runs, then glass is really eating up the light.

Another quick test of glass is to see how many layers it takes before you can't see through it. I know, you really can't do this unless your at a glass store. With some glass, you will not be able to see through the stack with just 5 pieces. That's 10% reduction in light per surface. Very high indeed. With coated 1% glass, the stack would have to be at least 50 pieces for the same condition to exist.

Larry

[ 06-21-2005, 11:50 AM: Message edited by: Larry Myers ]

Posted by John Pytlak (Member # 331) on 06-21-2005, 08:08 AM:

Poor quality glass not only "eats up" 10% or more of the light, but worse, it scatters light, causing flare and loss of contrast.

Posted by Dieter Depypere (Member # 3184) on 06-21-2005, 08:12 AM:

quote: John Pytlak
Poor quality glass not only "eats up" 10% or more of the light, but worse, it scatters light, causing flare and loss of contrast.

True. In the cinema, I am working, we have the phenomenon of the picture being reflected to the back wall of the booth. Also a sign for a glass which is not of the highest quality.

Posted by Dave Macaulay (Member # 813) on 06-21-2005, 09:41 AM:

The picture reflection isn't a sign of poor glass quality. Water white clear optical flat glass will reflect a beautiful image on the booth wall. Reflection is reduced by an antireflective coating applied to the glass surfaces. While this reduces the light lost to reflection, it's greatest contribution to screen image quality is the reduction - elimination really - of internal reflections in the glass that cause weird focus problems and image haloes where the image light goes through the glass at certain angles.
Coated glass needs to be treated carefully, the coating is relatively soft so anything abrasive (normal paper towel is pretty abrasive!) shouldn't be used. The coating may also be attacked by common chemical cleaners, ammonia is hard on some coatings so normal Windex might be a bad idea. Lens cleaner and non-abrasive paper or cloth should be used. There are "Kimwipe" products that are great but getting them from Kimberly Clark is a pain because of their distribution system; a salesman needs to come and try to sell your maintenance department a thousand different things. I've tried to call local distributors with exactly the SKU I want to order and been told to frig off more than once.

Posted by Alan Gouger (Member # 543) on 06-21-2005, 10:01 AM:

If using a single piece of glass any preference having it angled or flat?

Thanks!

Posted by John Pytlak (Member # 331) on 06-21-2005, 10:54 AM:

quote: Alan Gouger
If using a single piece of glass any preference having it angled or flat?

Always angled. You do not want to reflect the light directly back into the lens of the projector. For a single pane, a 7-degree tilt (with 0 degrees being perpendicular to the projection beam axis), reflecting the image upward, is a good choice.

http://www.cinemaequipmentsales.com/dolby9.html#6.6

quote:
Regardless of the wall structure, projector noise will escape through any single sheet of projection glass. port glasses should be angled to reduce lateral reflections; as a worst case example, internal reflections from a single port glass set at 90-degrees to the line from lens to screen will result in numerous reflections leading to a soft screen image apparently out-of-focus. A good result will be a front glass set at perhaps 7-degrees forward from the lens angle, and a rear (auditorium side) glass set at 15-degrees backwards.

Care should be taken over the quality of glass used, and optimum projection requires coating to further avoid internal reflections. (3)