Josh

1) Of course the front of the projector doesn't need to be 3 feet from the wall becasuse the only thing there is the lens and you need to keep the distance from the proj. to the port window to a minimum.

2) In a 2 machine set up, the 36 inches counts "concurrently" between the two. ie: You can have them 3 feet apart instead of 6 feet.

They also have to be installed in their own "permanent" enclosure which separates them completely from the audience. There has to be glass in the port window too. (I think there's an exception for the glass if the port is less than 12 inches square, but I'm not sure on that one.)

I don't know if that makes sense to you but that's what the code says. I don't think it necessarily applies to projectors set up in the home, excepting that all the other usual electrical codes need to be met.

A lot of the NEC for projectors seems to be throw-backs to the nitrate days.

If it were me, I'd have the projectors close enough together so I could reach both machines from the middle without having to take more than a step or two... Just enough room to manuver comfortably.

At changeover, if done correctly, the only thing the audience might have noticed was a color temperature difference because the arc target drifted a little while I was waiting for the cue marks. Sometimes, the carbon arc lamps had a spasm that could not be corrected until after the change-over.

Once you position yourself for a change-over in a carbon arc house, you stayed in that position. You did not reach around and scratch your butt, look at your target image, or whatever. You just stayed there until either the itch went away by itself, or the motor cues came by. I had hand operated sound change-overs, and foot operated picture changeovers in that booth. (A complete Brenkert booth.) You just concentrated on the upper right hand corner of the screen hoping the itch would go away.....

(now that should bring back some fond memories of you old carbon arc'ers)

And, if it was a major itch, it might be time for the annual flea-dip, or time to visit your "friendly" neighborhood Proctologist...

OK - I got carried away....but I think the angle offset of the projectors was 3 degrees maximum each, or maybe 6 degrees. Can someone verify the correct parameters on that? It has been a long time....

It was a 986 seat auditorium, with a 105 foot 4 inch throw.

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Some have tried using mirrors to keep the beams of two projectors on centerline (e.g.,"Ultra-Vision"), but IMHO, this is overkill, and brings in a whole new set of concerns.

Having discovered the Goldberg platter reel, in the spirit of trying to use the best of current technology, I wonder if a 3-projector booth or a 1-2-X where a projector is in the center position might not be preferable as from here there is -0- error?

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What I think you mean is Keystone distortion. Perspective change adapters or the eccentrics used in some projectors (eg Century SA) can be used to reduce or eliminate this sort of distortion.

Steve

A correctly designed theatre would minimize the off-center projection angle (down and horizontal angles), the lens offset (a large pupil lens to minimize vignetting), and the screen tilt.

>>> Phil

If you have a two machine setup, why couldn't there be such a thing as a "backwards" projector? The right hand machine could be made up so that it threaded up from (what is normally) the off-operator side. That way you can operate both projectors from the middle without having to run around to the other side.

Okay, you'd have the soundtrack on the inboard side of the projector and the reels and sprockets,etc would have to go backwards. Furthermore it would be a real bitch to remember to do one side backwards from the other.

Seems to me that the very short-throw large-screen houses with the booth up in God's country could use this technique to fool the system so the screen has a more of a head-on shot. It might be worth it just to reduce the obnoxious keystoning. I am sure the mirrors would be a bitch to clean, but if it works without too many problems, maybe it could be an answer, especially if the mirrors are made from optical glass.

Another wild thought - maybe a set of mirrors for each projector in a 2 projector operation might be practical in reducing side keystoning?

A bigger xenon bulb might be needed to allow for losses, but what the heck? If it works, it works!

Has anyone actually tried this? What were the results? Or, am I just dreaming? I'll almost bet some engineer who specialized in optics could throw in Finnigan's Finagling Factor and make it practical.

The big plus is that the inter-occular distance in only about 30 inches compared to the normal 60-72 inches. The result is a fantastic 3D image with minimal horizontal keystone distortion especially in short-throw theatres.

>>> Phil