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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?

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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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.

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.

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

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.

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.

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