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This topic comprises 2 pages: 1 2
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Author
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Topic: Port Glass Light Transmission
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Jay Glaus
Expert Film Handler
Posts: 123
From: Pittsburgh, PA USA
Registered: Dec 2010
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posted 11-27-2017 12:14 PM
Hi guys,
I belong to a drive-in group where it's members toss around ideas and suggestions. I came across an article one of their members posted and thought I'd toss it around here to see if it's really possible.
The guy said that he wanted a brighter picture, so he removed his port glass and his readings on the screen doubled.
Now, I use that OptiClear AR glass, which seems to do pretty well for me, I don't know what glass he is using but it is obviously some type of optic/AR glass as he stated about paying so much for the special glass, so he isn't just using plain old glass.
I know nothing is going to allow a solid 100% of light transmission, but I would expect optic glass to be around 90%-95%. And in a drive in type environment with all the dust kicked up from the cars theres always going to be a speck of dirt or two no matter how much you clean it. But it would just surprise me if it was cutting the light in half. Maybe I'm wrong. I do plan on trying it some night for a quick second and seeing.
He says he plans to run that way except for the really busy weekends in the summer. My exhaust fans are ~800cfm, and I can only imagine if I did that how much dust and dirt the negative pressure would suck into the booth, onto my lens, and I wouldn't even want to see the front filter. The only way I've thought it would even be possible to do is if you could take a piece of wood that fit in the window, cut out only the area your projected image actually hits so it is as small of an open area as possible, and place a couple of those blowers right around the window (on the inside) aimed at the little opening. Hopefully the blowers *might* be able to overcome the force of air wanting to come in, I'm not certain. But then again I'm also not certain I'm losing half of my light to my port glass.
Lastly, if you would like a little back story, the man that removed his port glass was using a 6k lamp, jumped up to Ushio's 7k, still wasn't happy and removed the glass. I have been using Ushio's 7k flamethrower for 2 years now, and aside from the 300hr warranty, I love it. I'm pretty happy with my brightness. I would always take more though if I could. The airport is right across the street (literally, you can see the planes on the tarmac) and the sky radiates orange from their light pollution. But this year was a little slow, laser is not in my budget yet.
So, does that sound possible to you guys? Just curious what everyone thinks.
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Steve Guttag
We forgot the crackers Gromit!!!
Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
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posted 11-27-2017 04:19 PM
Actual proper AR glass is going to be over 90% transmissive to the visible spectrum, when new. Opti-pure (distributed by Goldberg Brothers in the US and possibly others) is claimed to be 98% transmissive.
http://goldbergbrothers.com/movie-theater-products/projection-booth-equipment/optipure-glass/
Another popular supplier for our industry is Kelmar. From their catalog:
quote:
Kelmar 2X AR Coated Optical Port Glass in the new leader in Anti-reflection Port Glass. Unlike many similar Anti-reflective
products which are soft coat, Kelmar’s 2X AR Port Glass is a hard coat product which allows for easier handling, longer
shelf life and makes the Kelmar AR Port Glass an excellent choice for Projection windows that are subject to constant
cleaning. Kelmar’s 2X AR Anti-reflective coating increases the transmission efficiency to 98-99% as opposed to 92% for
uncoated glass. Glare is reduced as well from 8% to 0.5%
So again, we are at 98% (or more) transmission.
I'm not buying that one has doubled their light by merely removing the port glass if it was a proper port to begin with and it was being maintained properly.
My guess is that if you are using a 7KW lamp to get your light, you are probably using an NEC projector. They are about 20% less efficient than the Barco and Christie alternatives.
With a 7KW lamp you are also better served to get as big an aperture as you can (e.g. 4K in today's market) since the arc is so large, you get into etendue losses. As you move up in wattage, you progressively get less bang for the buck and more of your money goes up in heat rather than actual light throughput.
Another solution is to go to laser, including Laser-Phosphor. As one climbs above 4KW lamps, the cost effectiveness of laser progressively makes sense. The tough part for Drive-Ins is that short season. We have one in Maine and they'll get 2-seasons on a large xenon lamp. It would be at least 7-years before the balance between cost of xenon and laser-phosphor would even out. PIttsburg should be able to get a more reasonable season and quite possibly May through October with full schedules from June till Labor Day. Our drive-ins that run that sort of schedule are going through about 1 lamp a year in the 6KW. Payback on LP projectors is would be much faster for them. It would still take years but it would eventually get there.
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Carsten Kurz
Film God
Posts: 4340
From: Cologne, NRW, Germany
Registered: Aug 2009
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posted 11-27-2017 05:05 PM
Jay - if you really are using an optimized port glass, it makes little sense to go without it in a drive in, with all the negative implications. The question is - is that glass really good? Many companies sold port glass under fantasy names, and it may be that your glass nowadays has more like <90% transmission, whereas 98% to 99% is possible today.
Like Steve, I question the claim that the screen brightness doubled without a port glass. Of course, it IS possible if that glass has never seen cleaning or was of a very low quality.
In Europe, we typically use SCHOTT Mirogard or Amiran coatings on low iron oxide optiwhite glass.
I guess, for a drive-in, the port glass is not subject to fire regulations?
- Carsten
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Jay Glaus
Expert Film Handler
Posts: 123
From: Pittsburgh, PA USA
Registered: Dec 2010
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posted 11-27-2017 05:13 PM
Dave,
I'm interested to know how the differences are in your regular glass vs Optic glass installation, you'll have to let us know.
And Steve, I tossed around the laser idea, I'd love to do it but last time I checked it was still a little high. Maybe if last summer was a little better, but eh...
I have always wanted to upgrade my big screen to 4K for the aperture size to make the most of my 7kw for the 300 hours I have it. You ever seen a price for uplifting a 32B to 4K by chance? Just curious ball park what I'd be looking at.
Carsten, I too have a feeling that if he doubled his light from removing the glass, it can't be the same quality of port glass we are all using. On my big screen, I got my window that was a left over from an installation at a local indoor, I want to say the glass was made by Kelmar? A tech friend I knew had it. My other screens use OptiClear from Port Window Glass, as we had to construct our own windows into the other booths. I am pleased with all of my glass, my smaller (40ft) screens are lit nicely with 4kw and my big screen (80ft) is 7kw. I am going to try one night popping the glass out real quick and seeing the difference on the meter, but I can't imagine it can go up that much. I mean if it doubled I honestly think it would be too bright. But, nonetheless I was curious about all this as I am always trying to squeeze out as much light as possible.
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Jack Ondracek
Film God
Posts: 2348
From: Port Orchard, WA, USA
Registered: Oct 2002
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posted 11-28-2017 01:24 PM
Sam, yes. It was Martin. Don't know if he's still doing it though. It was several years ago that I heard he'd given it a try.
If you're already running some form of optical glass, I think you'll be disappointed in the difference you'll see, if any, when you pull it out.
I've been running single-strength window glass at my drive-in since I bought it in '86. Over the years, one window had to be replaced, so I had a chance to do a comparison. Yes... with that kind of glass, you can see a minor difference as you pull it out of the way, but it's not as significant as you might be hoping for.
My feeling was that the difference wasn't worth the problems not having the glass would cause, so the windows remain. I also don't think your audience would notice if you did pull them out, unless you did it as they were there. Even then, I doubt more than a few would wonder what just happened.
For me, it was like trying a 7kW bulb when I've been running 6.5s since I converted. The difference was definitely not worth the added cost and reduced warranty hours of the larger bulb.
If window glass is going to harm your presentation at all, it'll be if you have a piece that's so old it distorts your image or affects focus. We have a drive-in over here that's been projecting through double-pane efficiency windows since before they converted. The picture there has been horrible for years, but they haven't figured it out yet.
If, at 7kW, you're so marginally satisfied that you're looking for solutions, then start saving for laser. You probably won't be happy until you get one. For that matter though, nobody I talk to says the tech is ready for the kind of long-term lumen output we want to see from lasers at a drive-in.... but they might be ready within the next 5 years or so. I can handle that kind of wait.
I'm told that, to beat your 32Bs, you'd have to have the lasers running too close to capacity, and you'd be replacing them more often than you'll want to. Laser levels drop over time, too. In other words... compared to a 7kW xenon, you'll pay more to get the machine into your booth and you'll pay more to keep the quality of your image up.
Before I get flamed, I'm fully aware we have golden eyes here. Mine aren't bad, either. However, most of us drive-in operators are shooting 300+ feet at huge, white-painted walls, made of plywood or some form of roofing metal, producing, at best, a one-gain image. Many of us were blown away by the improvement digital brought to our places. For most of us, the difference between optical, or decent window glass, or nothing at all would be insignificant.
Interesting, the talk about 3D. Here we are, talking about the effects of port glass. One can only imagine what our pictures would look like, given the light loss 3D is responsible for.
As for polarity: Last I looked into it, only Dolby could be used on a "normal" drive-in screen... so long as you care to hand out glasses and post guards at each driveway to collect them... then wash, maintain, replace, etc. Heard someone had a "silvered paint", but wouldn't that just hotspot your center and make the side viewing angles much more dim? Given the angles at my place, I'd lose 40% of my capacity if silvering my screens does what it does at an indoor. The tempered glass argument has come up as well, possibly making the topic a non-starter.
Not one person has turned around and left my place because I wasn't running a show in 3D, so I think I'll worry about replacing the sinks in my restrooms this winter. :-)
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Dave Bird
Jedi Master Film Handler
Posts: 777
From: Perth, Ontario, Canada
Registered: Jun 2000
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posted 11-29-2017 10:09 AM
I'm hardly a "technical" guy when it comes to this stuff (more "mechanical", I loved 35mm)....I'm not sure I'll be able to tell the difference. I certainly made sure the new windows are single-pane, at least the side we'll project from, and I did get optical, however my recollection of when we calibrated the projector through the window glass was that our tech went through a number of adjustments to "color-correct" for our particular screen as it exists. Other than those "white scenes" where any flaws or degradation in the screen can appear (especially when wet), the colors look correct to me anyway, and the light meter says we're at spec. Like Jack says, the improvement was just so vast that I guess we just hadn't thought of it too much. I can say that in the rare cases where during a show a moth or something "splats" onto the glass and sticks there and I pull it out to clean, I can't say as I notice any difference at all in light level. Possibly see a faint line pass as the edge of the glass passes by, but that's about it.
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