Film-Tech Forum ARCHIVE: One Projector, Two Screens

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Posted by Paul Turner (Member # 832) on 01-03-2004, 01:57 PM:

I’m in the process of trying to get the city to let me convert a space to make into three or four more screens. One of the reasons the city is even considering this is I’m making the auditoriums very small – 50 seats each(I need a place to play out art house product). I have two Cinemeccanica V4s which are all set up to be interlocked. Now, being prone to thinking too much, I got to wondering if anyone had ever projected into two auditoriums with one projector by using a beam splitter and first surface mirror. Since my throws will be minimal and the projectors have 2k lamps, I figured light loss wouldn’t be a problem. I’d be worried about optical quality more than anything. Since I’m building the booths I can set ‘em up almost any way I want.
I did a quick search to see if anyone had written about this here. Nothing came up. Edmond Scientific has the beam splitters but their first surface mirrors are small. Any one have a source for these? Since this stuff seems relatively inexpensive, I figured I’d mess with it anyway. Just wondering if this road has been traveled before. Thanks.

Posted by Brad Miller (Member # 2) on 01-03-2004, 02:06 PM:

Why not 1 projector, 120 screens? [Big Grin]

Posted by Manny Knowles (Member # 1171) on 01-03-2004, 02:15 PM:

Since you're only going to show two movies, why not just build a twin instead of a quad?

Posted by Richard Fowler (Member # 893) on 01-03-2004, 02:26 PM:

It can be done but scale it out on paper since the final throw to each screen has to be the exact same distance due to focus. You may also have reversal factors using mirrors and beam splitter to hit a second screen. Large optical grade mylar tension front surface mirrors which are light weight are available from Hudson Photographic and Vutec. I have a rear projection set up that has been in operation for 9 years with a 3 x 5 foot mylar front surface mirror to a 10 x 20 foot screen.
The mirror is covered with a dust bag when not in use and is kept clean with compressed air.
In the end it may be better ( probably cheaper ) to get more projectors with a 500 - 1000 xenon lamphouse and interlock.

Posted by Paul Turner (Member # 832) on 01-03-2004, 02:48 PM:

Thanks for the input. I would love to do this as two larger auditoriums, but I’m dodging a body of regulation that would kick in as soon as the occupancy of each auditorium exceeds 49. If I go into that territory, I’m looking at $300k in building upgrades (it's only about 1/20th of that for another booth and aud). That story alone warrants a couple threads …
Mr. Fowler makes a good point: focus will be dependant on equal distance from lens to screen(s). I’m not sure how practical it would be though rack a screen back and forth for focus – though it might be stunning f/x during a boring film.
After looking at 120 screen drive-in, I feel I’m not as far out into the ozone as I suspected …

Posted by Manny Knowles (Member # 1171) on 01-03-2004, 07:09 PM:

Would this approach be within the realm of "film done right" ?

Posted by Paul Turner (Member # 832) on 01-04-2004, 01:06 AM:

Whether this can be "Film Done Right" is the question. The auditoriums will be to spec. I wanted to know if anyone else has done this, and how it came out. Rear projection can be "Film Done Right" and that process shares some characteristics of what I'm trying to do here. Again, thanks for your input.

Posted by Steve Guttag (Member # 268) on 01-04-2004, 01:57 PM:

The mirror beam splitter thing may prove to be quite annoying...you will have mirrors and a picture that is getting quite big. Also note, as the picture gets bigger, those mirrors will help magnify and vibrations.

Consider an "MPAA" delite system. Project on one screen and have a good quality video camera looking at that screen...then send the picture to a good video projector (a 50-seat rooms isn't going to be too taxing on a video projector). Then you will have your 2-screens for one and a means to play video sources too.

Steve

Posted by Manny Knowles (Member # 1171) on 01-04-2004, 02:23 PM:

Would the distributors really permit that?

I also wonder if there would be issues with people just not wanting to end up in the video room.

Why not leave those extra two theatres dark until you can outfit them with projectors of their own?

As each one opens, you have a perfect opportunity to turn it into a community event.

Posted by Peter Schoell (Member # 919) on 01-04-2004, 03:53 PM:

Steve's plan sounds interesting. I'm toying with a small "hold" screen and was going to use mirrors. As Steve suggested the second mirror would be quite big, and then there is the alignment to deal with.
Would you run into any sync problems with the video projected image?
Any suggestions for the video equipment?
For my situation this would work well because I could put the projector any where in the building and shoot the image onto as small a screen as possible, also a screen without holes.

Posted by Scott Norwood (Member # 30) on 01-04-2004, 06:56 PM:

For video, you would need either a 5-blade shutter for the projector or a 24P camera that can convert to 60i NTSC. Otherwise you will get flicker in the video image. Alternatively, you could run the film projector at 25fps and use a PAL camera and get a projector that can accept a PAL input (most can). A good video projector will probably cost as much as or more than a good rebuilt film projector, so it probably only makes sense to consider this if you want video capability anyway. Brad has a (relatively) inexpensive 24P camera and can probably answer any questions you might have about it.

Posted by Steve Guttag (Member # 268) on 01-04-2004, 08:49 PM:

I actually didn't invent the idea...there is a view-n-brew in this area that is using one film projector and 3-screens (2-video).

Now with a 50-seat room..how big is the screen? 8-feet tall? You could fool most of the people most of the time.

Heck with a 2KW lamp...a 5-wing shutter would probably still have enough light...

You could also have one telecine (projector with 5-wing shutter) and two video projectors so both are treated equally.

As to the distributors...so long as you don't duplicate the film (on storage media...like DVDs and such) it is no more offensive than running "interlock." What they want is the revenue from ticket sales and adding seating capacity only helps their cause.

Steve

Posted by Brad Miller (Member # 2) on 01-04-2004, 09:04 PM:

I can't possibly imagine the distributors permitting anyone to video(tape) a movie, even if it is just being used as an "interlock" sort of situation without a recording device. The whole thing would need to be set up to a pretty high degree of quality for it to be acceptable...and at that point what is preventing you from hooking up a VCR and recording it? Valenti probably loses his lunch at Wal-Mart just seeing blank videotapes. No way would he let such a thing pass. Besides, if you're going to go to that much trouble, it would be SO MUCH EASIER to just record the "bootleg" and play that tape back in the other auditorium with staggered show times. So long as you destroy the tape when you lose the movie, it's ok, right? NOPE!

I have a Panasonic DVX-100, which is a MiniDV 24P camera. I have done a test of pointing it at the screen during junk film and an empty gate. Indeed it is flickerless, as it is really capturing at 24P. There was some debate about how it was just simulating 24 frames per second, but nope, it really is 24P. At the resolution of DV, you're only looking at roughly DVD quality though. That's nowhere good enough for a second screen anyway.

And no Jack, I have never used it to pirate a film and never will!

Posted by Manny Knowles (Member # 1171) on 01-04-2004, 09:05 PM:

As far as I'm concerned, this notion of using video is just wrong. You're supposed to play the movie in the correct format and to a certain technical spec standard.

With that in mind, using video is not too different from playing a flat movie with a scope lens -- or even playing a stereo movie in mono (in this day and age).

And why do some movies (e.g. "Star Wars") come with a "no interlock" clause written into the contract?

Posted by Brad Miller (Member # 2) on 01-04-2004, 09:10 PM:

My only guess is that the film might get damaged or the movie would be played in a "lesser" auditorium. While I can understand not wanting the new Star Wars movie played in that mono house on opening week, any theater that knows how to take care of film will be able to handle an interlock without damaging it.

Anyone know the official reasoning?

Posted by Gordon McLeod (Member # 33) on 01-04-2004, 10:03 PM:

Multiple prnts mean multiple showtimes as a possibility which typical has ment higher revenue
(something that was always possible in a reel to reel multiplex)
( heck we bicycled StarTreck voyage home between 2 twins running it on each screen in 70mm and they were 10min drive apart)

Posted by John Pytlak (Member # 331) on 01-06-2004, 08:49 AM:

IMHO, interlocking 35mm projectors would be a much better (and likely much less expensive) option than video. NTSC video (even 24P) will not support viewing distances closer than about 4 to 5 screen heights --- in other words, if your screen is 8 feet high, the audience will likely not be satisfied with a video image if they sit closer than about 32 feet from the screen, not to mention the issues with properly projecting motion picture aspect ratios of 2.40:1 or 1.85:1.

If the theatres are any distance apart, the beamsplitter/mirror option becomes quite impractical as the physical size of the mirror becomes very large more than a few feet from the projector.

Posted by Paul Turner (Member # 832) on 01-06-2004, 12:17 PM:

This might give a better idea of what I'm talking about. I scaned part of an early version of the plans. Nothing is to scale. I think this design will keep the splitter and mirror to a resonable size. Both auds are for about 45 seats. Placement of the projector can get both screens the same distance from lens.
I like the video idea, but I think set up would look better -- and it would be film.

Posted by Gordon McLeod (Member # 33) on 01-06-2004, 12:29 PM:

You will need to invert the image going to the second screen

Posted by John Pytlak (Member # 331) on 01-06-2004, 12:56 PM:

The image through the beamsplitter mirror is normal orientation. The reflected image goes through two reflections, so it will also have the correct orientation.

Looks workable, except that the beamsplitter, mirror, and ports will likely have to be quite large and unwieldy. As mentioned, vibration may be your worst enemy, as well as keeping such large optical surfaces clean. Be sure your mirrors are front-surface, along with an anti-reflection coating on the backside of the beamsplitter to minimize flare or a double image. Have the operating side of the projector face the door, so you have access without having to duck under the beam.

Posted by Dominic Case (Member # 1830) on 01-06-2004, 09:29 PM:

You probably would have enough light for the small screens, but remember that, as with focus, you have to have the two screens both correctly illuminated with the same lamp setting. If your half-silvered mirror (beam splitter) is exactly 50/50 and there is NO light loss from your second (front-silvered) mirror, then all would be OK - but you still need exactly twice the light output that you would for a single screen.

Posted by Steve Kraus (Member # 476) on 01-06-2004, 10:01 PM:

This is lots of fun to talk about but the reality is that it makes so much more sense to set up two projectors even if it means scrounging to get some acceptable old gear. Picture quality will be better and you will gain enormous flexibility using the theatres separately or together as needed. Platter can be a 5 deck if space is too tight for separate units. It would be a shame to go to all this trouble to equip two separate theatres and then not be able to use them as such. Your plan compromises image quality and probably sound quality as well unless you have separate EQ for each house.

Posted by Mark Gulbrandsen (Member # 72) on 01-06-2004, 10:11 PM:

I've been watching this thread and have been pretty amused at things that were suggested but in your case the second projector and sound system is definately in order. Even an older machine would be a better choice than anything else that I've seen suggested here. Old equipment can also look very good on screen and if pampered can last a loooong time...ok, its made it this far in time hasn't it?
Anyway, at least making an effort towards film done right is far better than an image and sound done half assed. Your customers will also appreciate it and come back for a repeat.
Consider also installing an LCD video projector in ONE auditorium for more flexibility.

Mark @ CLACO

Posted by Brad Miller (Member # 2) on 01-06-2004, 11:03 PM:

Well if you simply MUST go with one projector, at least "double stack" your digital readers so you can send one reader's feed to one sound rack and the other reader's feed to the second sound rack. It would also be unbelieveably handy when it comes time to troubleshoot. [Big Grin]

I'm in agreement here though, you're looking at the cost of a projector, console and automation for that second screen. If you got in a daily routine of interlocking, you would find that after a few days it would be such a "regular thing" that you wouldn't think twice about it. Plus if you take Steve's advice of a 5 deck platter, you can always become a "3 plex" booking-wise during the slow seasons. Heck, on weekdays you could stagger the auditoriums. A 2 hour movie could run in #1 at 7:00 with your next showtime of 9:10 in #2. That eliminates you from having to keep somebody on staff specifically to clean the auditoriums since you would be staggering the shows between the two auditoriums. During the middle part of the movie, you could clean the auditorium not in use. It would also chop off an easy 1/2 hour of your payroll by eliminating the downtime between shows.

If you want to get weird though, here's my Guttag-themed suggestion. Set up 3 projectors, all of which are able to rotate 180 degrees to point between the two auditoriums and all have their own set of aperture plates for the specific auditorium. Start reel 1 on projector 1 in auditorium 1, then changeover to projector 2 in auditorium 1. 1/2way through reel 2, you will have rotated projector 1 180 degrees and start that same reel 1 (with appropriate aperture plate) to auditorium 2. Meanwhile you will do your changeover from reel 2 to reel 3, changing over from projector 2 to 3 in auditorium 1. Of course then you must flip projector 2 around to auditorium 2 and get things set for your changeover (rewind and rethread reel / change aperture). Do the changeover in auditorium 2 from reel 1 on projector 1 to reel 2 on projector 2, then load up reel 4 on projector 1 and rotate it back to auditorium 1 (don't forget that aperture). When reel 3 on projector 3 is over in auditorium 1, do the changeover from projector 3 back to projector 1, so you are changing from reel 3 to 4. Then rotate projector 3 to auditorium 2 and reset reel 3 on it, swap the apertures and do your changeover from projector 2 running reel 2 to projector 3 running reel 3 all in auditorium 2. Need I continue? It's super simple, it gives you that fabulous "changeover presentation", it staggers your showtimes and it saves you the cost of buying that 4th projector for your 2 screen. (As an added bonus you can see how this is clearly an easier solution to interlocking with those pesky platters.)

Genius!!! [steve]

Posted by Paul Turner (Member # 832) on 01-07-2004, 02:51 PM:

I think I'll take Brad's suggestion about flipping the projectors 180 degrees and just sell tickets to watch the booth. Reverse the ramps and point the seats away from the screen. No film rental -- just run trailers! Anything to cut payroll.

Great input from the group. Since I have a matching Cinemeccanica, I'll interlock. But don't think I'm not going to try the beamsplitter first ... And I actually like older machines (Motiograph AA and RCA 9030 running seven years with NO problems) and can find a couple I can put into service. I'll post a follow-up when I try the split before I put in the second projector. Thanks!

Posted by David Graham Rose (Member # 1450) on 01-08-2004, 03:25 PM:

Greetings from Cambridge

I believe you are heading down a very slippery slope my dear boy. Unless both screens are one hundred percent identical, and that inculdes light paths, keystone angles and rake, then the image will never be focussed correctly.

I have done a myriad of experiments of this nature here in the Departmenty of Cinema Technology, and have found that angle, and rake are key factors in image distortion*ref1. The majority of the funding originated from one of the UK's largest cinema chains, but due to poor field trials, the idea was never implemented.

*ref1 Acta Cinematogrfia Vol 105, pp 34-76, auth. Harris-Quelch, Ryder, Weir & Rait

Your with many high grade silver mirrors in store

David

Posted by Paul Turner (Member # 832) on 01-10-2004, 04:39 PM:

I've decided I'm just going to get a couple projectors and interlink for presentation to the public. But, before I open my doors I will fool around with it and see what happens. Be a great way to kill half a day (before I rock and insulate the booth walls). Right now the city hasn't even issued permits so I have plenty of time to do some research before striking the lamp. I want to see if I can fine-focus screen two by altering the distance between the splitter and the mirror and stuff like that. I'll post when I've given it a shot.