Film-Tech Forum ARCHIVE: Does a drive-in movie theater use the same type of projection window as a

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Posted by Don E. Nelson (Member # 1049) on 03-04-2005, 02:39 PM:

I was wondering if a drive-in movie theater uses the same type of projection window as a conventional sit-in theater. I am currently projecting both 16mm and 35mm without a window, but reel soon my 16/35mm booth will be done (mainly to isolate the projector sound from the audience) and I need to start thinking about the window design and fabrication. What should I mostly be concerned about(optically) when constructing this projection isolation window for my outdoor theater.I run dual Universal Proj. Co. units with Schneider flat/scope lens and 3000 ft. reels.

Posted by John Vincent, Jr. (Member # 1791) on 03-04-2005, 03:07 PM:

Depends. I've seen Drive-In's do it with port glass and without. We do it without (just open - no loss of light). There is a blower set up to push air outside through the opening to prevent bugs from entering.

Posted by John Walsh (Member # 168) on 03-04-2005, 04:09 PM:

You might be interested in reading the topic: "Clear optical port glass"
You can find it using the search feature.

Posted by John Pytlak (Member # 331) on 03-04-2005, 04:14 PM:

A drive-in does not need sound isolation, so port glass is optional, and double-glazing (two panes) is totally unnecessary. As others have noted, "bug blowers" can be used to keep the insects out (some love the bright light from the lens), with no attenuation of light output.

Because most drive-ins struggle to get enough light on their huge screens, if port glass is used, be sure it has anti-reflection coatings for maximum light transmission.

Posted by Justin West (Member # 920) on 03-04-2005, 09:02 PM:

How about clear, 1/4" thick plexiglas?

Posted by Mike Blakesley (Member # 26) on 03-04-2005, 10:49 PM:

NO! Plexiglass will distort your image AND soak up light. Unless there's some kind of super whizbang optical plexiglass I've never heard of. (Which wouldn't surprise me, being here in Montana.)

Posted by Phil Blake (Member # 2012) on 03-05-2005, 04:36 AM:

We never had port glasses in during the show at either of my drive in's.

We had a piece of sheet metal cut with an opening just big enough to let the image beam through , this was slid into the port opening to reduce wind and rain coming in , the glass would only go in at the end of the night.

We never had any bug blowers , did not know they existed then , consequently to shutter blades were kept very busy during the night slicing and dicing bugs . I was shocked when removing a shutter housing for a timing adjustment , the inside of the housing resembled a lawn mower catcher! it held over 10 years of MIA bugs .

From memory the size and location of the ports were very similar to indoor cinemas I have been with.

Posted by Ken Layton (Member # 133) on 03-05-2005, 08:49 AM:

Many drive-ins use no glass at all because the glass eats up precious light. At the now demolished Sunset Drive-in Theater in Tumwater, Washington we had a sheet metal box with an opening just big enough for the image to get through on the front wall.

Posted by Richard Fowler (Member # 893) on 03-05-2005, 01:13 PM:

Xetron many years ago sold a plexiglas window with or without anti-reflective coating. You can get optical like grade in plexi / perspex and I have seen uses in photographic work....but the item for cinemas was shortly abandoned since it was prone to scratches and static.....maybe the Montana air was too dry [Big Grin]

Posted by Tim Reed (Member # 137) on 03-05-2005, 11:18 PM:

Re: Plexi-Glas... Actually, the thicker varieties (1/4" and up) are not bad, and a good alternative to optical glass for the money. It has high transmittance and parallel surfaces. The trick to keeping it scratch-free is to clean it infrequently, and carefully. Even better is to use a lens blower/brush on it.

The thin stuff is terrible, though. Pure crap.

Either kind, however, is lacking in the noise-isolation department.

Posted by Frank Angel (Member # 248) on 03-07-2005, 12:33 AM:

I have had good success with Lexan, a brand name plexi which seems to have a harder surface than generic plexi and thus less susceptible to scratches which is a property where optical glass wins over plexi. Our Lexan has lasted for a decade before I decided it needed replacement. I treated it as if it were a lens, cleaning it only with camel hair bush and then when it got any grim on it, cleaned it with diluted dishwashing solution. If you are the only one messing with it, you can keep a Lexan port a as scratch free as any glass window.

Although I have never seen any stats on it but it, I don't believe Lexan causes any color or geometric distortion (at least not the 1/4in thickness variety). If you look at the edge when light is passing through plexi, the edge lights up white. This is what water clear glass looks like so I am assuming it has at least as good transmission properties as water clear. On the other hand, light dissipating at the edge indicates that there is some internal light scattering, although my experience has been that it doesn't cause any significant loss or contrast degradation, if you are in a situation where every last fraction of a footlambert is critical, then go with high quality, double surface coated optical glass -- but you'll pay a lot more for it.

Posted by Kenneth Wuepper (Member # 1174) on 03-07-2005, 06:54 AM:

Our experience with "plexi" material is from the spotlight booth in our local civic auditorium where the safety people made them install shatterproof material. The front of the booth is the size of a pair of patio doors and at a 24 degree down angle. The material had to be strong enough to stop the fall of an operator if balance was lost and the operator fell against the angled surface. The enclosure also had to keep the hot carbons from the super troopers from bouncing off the cement floor and out on the audience.

The problem with this (hockey dash grade) plexi was the fact that it diffused the light and made the spot edges fuzzy. It also became very yellow where the light beam went through it on a regular basis. The two pieces of new hockey dash were for replacement in the arena at the other end of the facility.

Our local drive-in booth was at ground level and the unglassed ports for projection had large "eyelids" for weather. A large pointed area in front of the booth was grass with a fence to keep people walking to the concession stand from interrupting the projector beam.

KEN

Posted by Brent Neal Jones (Member # 1048) on 03-07-2005, 02:27 PM:

We run without the glass, and then replace it each evening.

Posted by John H. Crawford (Member # 3086) on 08-19-2005, 12:17 PM:

Regarding port glass, a twin theater I know of, The Grand in Du Quoin has NO port glass whatsoever... which means you are subjected to hearing the projector throughout the whole show.

BTW this theater has some cool projectors, Brenkert BX-60 in the upstairs auditorium (this was built in the balcony) mated to an "ancient" Christie 1kw lamphouse (a H-10 I believe) and has Strong platters (old one,it has white rollers), and a Super Simplex in the lower auditorium, mated to a Lume-X, and has an ORC "Super" platter.

[ 08-20-2005, 03:00 PM: Message edited by: John H. Crawford ]

Posted by Monte L Fullmer (Member # 2797) on 08-19-2005, 02:01 PM:

quote:
Strong platters (old one,it has white rollers),

...That'd be an old Balco platter-a Ballantyne platter that eventually became the Strong A-3 (Alpha) platter after serious modifications.. - Monte