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» Film-Tech Forum   » Operations   » Film Handlers' Forum   » Rear projection cinemas (Page 1)

 
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Author Topic: Rear projection cinemas
Howard Johnson
Film Handler

Posts: 87
From: Felpham , West Sussex, UK
Registered: Jun 99


 - posted 04-19-2002 05:54 AM      Profile for Howard Johnson   Email Howard Johnson   Send New Private Message       Edit/Delete Post 
One of the cinemas where I work is thinking of adding a second screen, however there are space restrictions and they are thinking of making it back projection with the projector to one side of the stage and projecting onto the back of the screen via a mirror set at 45 degrees which would make a throw of about 21 feet with a scope screen 11 ft. wide. You won't be able to have the speakers behind the screen there will be a light loss using the mirror and it will need a very short focal length lens which might make distortion. are there any other problems to consider and are there any such cinemas in the UK?

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Dick Vaughan
Phenomenal Film Handler

Posts: 1032
From: Bradford, West Yorkshire, UK
Registered: Jul 2000


 - posted 04-19-2002 06:35 AM      Profile for Dick Vaughan   Author's Homepage   Email Dick Vaughan   Send New Private Message       Edit/Delete Post 
Howard

The mirror should be surface silvered to prevent double imaging and dependent on where it is situated in the light path could be both very large and very expensive.

One thought that occurs to me is who is responsible for focus?

Are you thinking of remoting this to a control point in the auditorium and letting the ushers adjust it?

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Pete Naples
Phenomenal Film Handler

Posts: 1544
From: Dunfermline, Scotland
Registered: Feb 2001


 - posted 04-19-2002 06:38 AM      Profile for Pete Naples   Email Pete Naples   Send New Private Message       Edit/Delete Post 
Howard, it can be done! There is at least one rear projection screen in the UK. Kinema in the Woods, Woodhall Spa, Lincolnshire is the only one I know of for sure. It's on the old WWII airfield that the dambusters flew from, built of nissen huts and runs Kalee projectors. Two screens, one is rear projection done just as you described, the other is front projection. Also has a working organ and organist. it's quite a place, well worth a visit, I can't remember the owners name, but he's a nice bloke and quite approachable. A colleague and I installed DOlby in both screens, the rear projection one has the LF cabs below the picture and the horns flown above, not perfect but works ok. Problems I know he has with rear projection are mirrors, you really need to use a good quality optically flat silver mirror, which are expensive and get killed by dust easily. If you use a standard bathroom mirror you lose a lot of light and sharpness. Also I noticed that the picture was quite dark towards the edges. Rear projection screens are relatively easy to come by, as rear proj is used a good deal in AV, conferencing etc.
Woodhall Spa is a lovely wee place, I stayed in a hotel near the cinema, the bar of which had been the officers mess for the dambusters squadron. The walls are covered in aeronautical memoribilia, some local enthusiasts are restoring a Lancaster bomber to flying condition, last time my colleague was there he'd seen the spectacle of it taxi'ing around on three out of four engines. That's a couple of years ago now, so it may well be flying by now.


Didn't Kalee build a reversed projector for rear projection WITHOUT the mirror??. ie The soundtrack ran on the inboard side. I'm sure somebody told me that years ago and that there were a pair running in London somewhere. Wish I could remember who told me that now!


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Howard Johnson
Film Handler

Posts: 87
From: Felpham , West Sussex, UK
Registered: Jun 99


 - posted 04-19-2002 08:21 AM      Profile for Howard Johnson   Email Howard Johnson   Send New Private Message       Edit/Delete Post 
Thanks Dick and Pete, I was also wondering about focussing, would a video camera located at back of auditorium be clear enough? Otherwise your suggestion of a remote focus control sounds good.

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Richard Fowler
Film God

Posts: 2389
From: Ft. Lauderdale, FL, USA
Registered: Jun 2001


 - posted 04-19-2002 08:36 AM      Profile for Richard Fowler   Email Richard Fowler   Send New Private Message       Edit/Delete Post 
There are rear projection mirrors availble made of mylar sheeting mounted to a aluminum frame under tension which gives a "first surface" image for sharpness( made by companies such as Hudson Photographic Industries or Vutec; I believe it is a British patent )...the light loss is about 3 to 7%; they are light weight and we have used them on rear projection displays with an average of 12 to 16 foot width. We usually give a customer a spare mirror in case of unfortunate damage. The projection screen surface must be picked with care based on your situation since there are different types / image gain available in flexible PVC, rigid plastic or glass....the better the surface...the better the image. You will also have to contend with hot spot of the image due to short throws. There is a little trick....take a piece of paper, if you know your lens throw to final image, you make a drawing from the point source of the projector to the final image size to scale ( I was trained as a draftman ) this will yeild a "triangle" type image, which when cut out can be folded to see available angles, mirror size, projector and screen location to give you a preliminary feel of what can possibly work in the situation;.
Richard Fowler
TVP-theatre & Video Prdoucts Inc. www.tvpmiami.com

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Frank Angel
Film God

Posts: 5198
From: Brooklyn NY USA
Registered: Dec 1999


 - posted 04-19-2002 08:39 AM      Profile for Frank Angel   Author's Homepage   Email Frank Angel   Send New Private Message       Edit/Delete Post 
Yes, it can be done, just like the Jerry Lewis theatres used 16mm. It can be done but with substandard results.

Biggest problem is the mirrors, no, the biggest problem is the light fall off, no, it's the operating noise, no...ah -- it's everything....EVERYTHING is a big problem.

First the mirrors -- they collect dust and are a chore getting aligned, almost impossible to avoid keystoning. You try to clean them and accidently nudge one a little to much and your are in alignment hell all over again.

Second, forget about getting uniform screen illumination -- difficult with flat picture, absolutely impossible with scope; the light distribution characteristics of the screen material itself is that it creates a hotspot with short focal length lenses, which is what you have to use with an RS settup, The hotspot moves from left to right, depending on where you are sitting. The one theatre that used rear screen here in Brooklyn (the only one I know of and which closed in 1980) only ran flat because the scope image was so terrible.

Then there's the question of sound. Projector sound -- the only thing between the projector and the audience is a huge expanse of screen material that is not at all soundproof. Unless you build a room around the projector, then it's just a noisey machine basically sitting in the same acoustical space as the audience. And then the soundtrack sound -- where do you place the speakers? Certainly not in the center of the screen so on the sides, over screen? Where ever you put them, they won't be in the ideal location, i.e., BEHIDE the screen so the audience has the illusion that the sound is coming from the image.

The veteran union projectionist who ran this rear screen here told me that it was the worst place to work and it was difficult for him to get vacation relief because when any projectionist saw that theatre up on the call board, no one would sign up for it.

There is a reason that there are 9000 screens in the US and none of them use a rear projecton system. It is an ill-conceived idea from the get-go any you can bet anyone opting for it will be plagued with heartburn for years to come. Why would anyone choose to do film wrong right out of the starting gate?

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Bernard Tonks
Jedi Master Film Handler

Posts: 619
From: Cranleigh, Surrey, England
Registered: Apr 2001


 - posted 04-19-2002 09:00 AM      Profile for Bernard Tonks   Email Bernard Tonks   Send New Private Message       Edit/Delete Post 
Pete,

Cinemas in London I know that had rear projection, one was the Rank Odeon owned Palace in Tottenham, an old variety theatre, sure they were Kalee 21s with special optics without the mirror. There was the Compton Cinema Club in London's Soho with Kalee 37s facing each other behind the screen, but that was a strange set-up as I'm sure the picture was mirrored onto the front of the screen. When the Waterloo Station News Theatre first opened, that was also a mirror system to overcome keystone, but was abandoned later in favour of raking the projectors for a direct throw.

I have also visited the Kinema in the Woods, a must place to visit, and as Pete said, the owner Ken Green, (I believe), is very friendly indeed.

Screens 2 & 3 in the old Odeon Guildford was rear projection, one with a mirror, the other direct without.


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Mark Ogden
Jedi Master Film Handler

Posts: 869
From: Little Falls, N.J.
Registered: Jun 99


 - posted 04-19-2002 09:44 AM      Profile for Mark Ogden   Email Mark Ogden   Send New Private Message       Edit/Delete Post 
Frank: make that 8999 and 1. The highly popular Brattle Theatre near Harvard University in Boston is a single screen rear projection set up, mostly as a design compromise in a turn of the century building.

And while it's not America per se, I belive some of the screens at the Eaton Centre in Toronto are still RP. There are some pictures of this in the warehouse, I belive


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Pete Naples
Phenomenal Film Handler

Posts: 1544
From: Dunfermline, Scotland
Registered: Feb 2001


 - posted 04-19-2002 09:59 AM      Profile for Pete Naples   Email Pete Naples   Send New Private Message       Edit/Delete Post 
Thanks Bernard, I had a feeling you'd know. The Waterloo news theatre rings a bell as being the place with the reversed Kalees. I must ask around and see who told me that little gem Thanks also for remembering Ken Green's name, I had it into my head his name was Jimmy Green for some reason.

Frank, you are the prophet of doom and gloom! For some cinemas, adding a screen, even a sub standard screen, is the difference between life and death. Projector noise need not be an issue, indeed at Kinema it isn't, as there is a booth of sorts, with a port in front of the mech. The Cameo in Edinburgh added two mini's some years abck, these were converted out of shop units to either side of the original auditoreum, and part of the back row was lost to form the cross corridor. Now those theatres have tiny pictures, you can hear the mechs as the port glass isn't too good, and the speakers are so close together you can't really tell it's stereo, but those two little boxes of 66 and 77 seats keep the place open when there's not the product to fill the main screen.

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Scott Norwood
Film God

Posts: 7976
From: Boston, MA. USA (1774.21 miles northeast of Dallas)
Registered: Jun 99


 - posted 04-19-2002 10:28 AM      Profile for Scott Norwood   Author's Homepage   Email Scott Norwood   Send New Private Message       Edit/Delete Post 
Yeah, the Brattle setup is really bizarre. The projectors are parallel to the screen and face each other. There is a pair of 45-degree mirrors between them to direct the image to the screen. They also have a 16mm projector that requires putting a third mirror in place. The booth is in its own room for sound isolation (with a huge window that covers most of the front wall), but booth noises still often leak through. They recently installed a new screen which seems pretty good.

Overall, image quality is OK and better than one might expect for rear projection. I know a couple of people who used to work there; apparently framing is sometimes a problem because the edges of the masking aren't visible from the booth (and they use top masking). Sound quality is an issue: they used to have mono sound with a speaker on either side of the screen; now they have Dolby with the center channel speaker mounted above the screen. It's OK, but not great, although most of what they show is mono anyway.

Are there any other rear-projection setups in commercial theatres in the US? Surely there must be some place that has one.


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Jerry Chase
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Posts: 1068
From: Margate, FL, USA
Registered: Nov 2000


 - posted 04-19-2002 12:42 PM      Profile for Jerry Chase   Author's Homepage     Send New Private Message       Edit/Delete Post 
I did the math once, long ago, and found that a first surface mirror isn't going to make any major difference in standard throws - provided - that the mirror is located at least 10 feet away from the lens on short throws (60 ft or less), and further away on long throws.

Greg Muller or Evans could probably do the math. I remember I was surprised at the time how little difference front and rear surface made once you got away from the lens. There is some additional light drop, but not much more than if you pushed the screen a few feet back.

The big issues I've seen with rear projection are the hot spot, and sometimes a color cast from the screen material. Don't underestimate the hot spot problem on a short throw. Think of how the rays of light hitting the back of the screen are really splayed out at the edges. They will diffuse because of the screen material, but the brightest angle will always be the one directly leading through the screen to the lens. A fresnel lens screen would be the best way to reduce the problem, but the cost would be outrageous even if you could find one that large. Eliminating the fresnel possibility, there are RP screens that are much better than others through use of encapsulated spheres and other tricks. Don't even consider going with a cheap screen like frosted plastic. Folding the light path at least once to increase the throw will reduce the hot spot problem some, but that will mean more mirrors.

If the bright spot is just too much of a problem, you could experiment with placing a neutral density filter a few inches in front of the lens to darken the center of the image. It is messy, a light sucker, and a kludge, but it can help.

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Steve Kraus
Film God

Posts: 4053
From: Chicago, IL, USA
Registered: May 2000


 - posted 04-19-2002 12:55 PM      Profile for Steve Kraus     Send New Private Message       Edit/Delete Post 
It's hard to imagine a constraint so severe that RP would become worth the hassle. That's a very large space you need behind the screen. Surely there is some way to carve out a small booth at the rear and put all that space to use within the occupied auditorium.

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Gordon McLeod
Film God

Posts: 9448
From: Toronto Ontario Canada
Registered: Jun 99


 - posted 04-19-2002 07:17 PM      Profile for Gordon McLeod   Email Gordon McLeod   Send New Private Message       Edit/Delete Post 
Cineplex Odeons first theatre "The Eatons Centre" in Toronto was 18 screens all rear projection (now closed)
pictures are in the picture warehouse

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Rick Long Jr
Expert Film Handler

Posts: 211
From: Toronto, Canada
Registered: Jul 2000


 - posted 04-19-2002 08:44 PM      Profile for Rick Long Jr   Email Rick Long Jr   Send New Private Message       Edit/Delete Post 
I was projectionist for while at the Eaton Centre. Quite an interesting place to work in more ways than you can concieve. Most of the booths were separate rooms. The rear projection auditoriums were built with the booth at the front about 20 feet long by about 6 or 7 feet deep. The Prevost P-55's shot onto the first mirror(2 ft by 4 ft) about 6 feet or so from the lens. This mirror reflected the image at 45 degrees to a mirror mounted directly under the screen tilted back at about 30 or so degrees to another large mirror mounted on the back wall up above the projector, reflecting the image to frosted screens (installed with the smooth side toward the audience to make it easier to clean the Coke off.) The best way to focus was to get down beside the machine and look at the image in the first mirror. Yeah, It worked, but not very well. Most were converted to 1k lamps, but when I closed the place they were still using a 500 watt in C-10. The light always had a wandering hot spot that followed you around the auditorium. Sound was provided by two home stereo speakers built into the wall at each side of the screen(mono sound). They also had some interesting periscope booths, but that's another story.

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Matthew Bailey
Master Film Handler

Posts: 461
From: Port Arthur,TX
Registered: Sep 2000


 - posted 04-19-2002 09:00 PM      Profile for Matthew Bailey   Email Matthew Bailey   Send New Private Message       Edit/Delete Post 
Did anyone as I recall have a post on here on the GNB projectors used for rear projection aboard a ship? Would there be anything required with using one with a platter?

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