Film-Tech Forum ARCHIVE: Strip screen Alignment Plate/Guide

This is topic Strip screen Alignment Plate/Guide in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Mark Gulbrandsen (Member # 72) on 02-09-2003, 09:15 PM:

Am looking for a clear photo of one of these to be able to replicate them. I have a photo I took at the Cinestage in Chicago before demolition began, but its not quite clear enough to really tell the size of them. They are about in the center of the photo. What did they use in Bradford?
Mark

Posted by Steve Kraus (Member # 476) on 02-10-2003, 12:19 AM:

I have a blurry photo also taken at the Cinestage which may give you a better idea. Click on "Strip Alignment Plates."
http://steve.filmteknik.com/cinestage.html

It's just sheet metal with slots notched into it a bit wider than the strip and there's a part at the end that comes back around in front of the strip a little bit. The difficulty would stem from the fact that they all need to be slightly differently angled.

Unless you have a good way to make this (surely the originals were done with some sort of punch press operation) it might be better to come up with a different sort of design, maybe with individual moveable guide pieces screwed to master plate segments. Then they could be individually adjusted in the field to the precise angle and the screw tightened down. Many more pieces involved but they'd all be the same, just crank them out en masse and no chance that you find out too late that the angle was miscalculated. I believe you need them halfway up as well as top and bottom if it's a large screen.

Steve G will correct me if I'm wrong but I understood that the Uptown's are still in place albeit bent up out of the way of the sheet screen.

Posted by Stephen Furley (Member # 1277) on 02-10-2003, 05:36 AM:

Why not contact John Harvey? Surely he would have the information you need.

Posted by Steve Guttag (Member # 268) on 02-10-2003, 08:26 AM:

I actually have a section of the guides in the Uptown booth! If I remember, I'll snap a close up of them this weekend.

Steve

Posted by Mark Gulbrandsen (Member # 72) on 02-10-2003, 08:33 AM:

Apparently John Harvey doesn't know either, or isn't bothering to provide the info. I guess if he did, they would probably have used them on the Dayton screen. The cross reflection was pretty bad there.

The strip screen in Seattle is in dire need of these guides. John also has worked with them as well but they have no guide plates on an over 90 foot wide screen! The strips flap in the beeeze so to say....when the HVAC is running. Makes showing 3-strip a bit difficult. The HVAC has to be shut down durung a show.
Steve K mentioned....
"Unless you have a good way to make this (surely the originals were done with some sort of punch press operation) it might be better to come up with a different sort of design, maybe with individual moveable guide pieces screwed to master plate segments. Then they could be individually adjusted in the field to the precise angle and the screw tightened down."
Thats exactly what I want to look into doing. There is also another location that could be set back up very easily to run 3-strip here in Salt Lake City just by re-installing a strip screen. Everything is there on the original frame except the alignment strips. I agree that some sort of individually movable per strip guide is probably the best route. Having the parts made via a punch press is not a problem. There could be an angle refrence stappmed into each plate at each guides location to enable proper alignment of each strip at top, center, and bottom.
Mark @ CLACO

Posted by John Pytlak (Member # 331) on 02-10-2003, 08:51 AM:

In theory, if a typical gain material was used for the screen, shouldn't the optimum angle be deterimined by ray tracing, to reflect each projector's light back to the "sweet spot" of the seating area? If a matte white screen material was used, the angle of each strip would not matter much, since matte screen material reflects light diffusely, in a wide pattern.

Does anyone have specs for the original material used for the strips?

Posted by Mark Gulbrandsen (Member # 72) on 02-10-2003, 09:09 AM:

John, The material was indeed a cloth backed embossed lenticuluar material of some sort, not matte white. I have a partial strip from the Cinestage in Chicago. Interestingly enough the Cinestage opened with a solid sheet as designed by Todd-AO. I believe it was in fact the second or third installation of Todd-AO. Eventually the solid sheet was removed in favor of a strip screen. This screen was not very large...perhaps 60 feet on the curve, so I think being smaller. it may have suffered from cross reflection even worse than larger screens would have. In Thomas Haurslev's article on Todd-AO he talks about the problems AO had designing the screen. This screen surface and frame was eventually patented!
Michael Todd musta had permission from Cinerama, or perhaps as part of the deal when he left Cinerama to use some of its design in his system.
Below is a photo of the Cinestage screen before demolition of the main building began. I was there to photograph it and study its design....sadly I forgot the most important part of it.
Note also the alignment strip thats horizontal about 2/3's of the way up the screen. Quite a bit of the top of this screen is masked off for what ever reason. The back of the screen to the right was for running pornos on, which the theatre did for over a decade before it closed.
Mark @ CLACO

Posted by John Pytlak (Member # 331) on 02-10-2003, 09:22 AM:

Mark: If you have a reasonable length of the material, it may be possible to have a screen manufacturer put enough of them together into a "sheet" and use a reflectance goniometer to measure the reflectance pattern (gain as a function of viewing angle) of the material. Would be nice to document what the material actually was.

http://physics.nist.gov/Divisions/Div844/facilities/specphoto/facilities.html

Posted by Ben Wales (Member # 92) on 02-10-2003, 02:57 PM:

Mark,

I have some some spare original Cinerama (1967) strips and could send you one (drop me a email) the material is thicker than the one used at the Cinerama at Bradford.

Posted by Steve Kraus (Member # 476) on 02-10-2003, 05:28 PM:

Mark wrote:
Having the parts made via a punch press is not a problem. There could be an angle refrence stappmed into each plate at each guides location to enable proper alignment of each strip at top, center, and bottom.

Perhaps, as long as each set of top, bottom, and center plates is custom made with the proper angles for each strip. In the middle the strips are following the curve of the screen but as you move to either side they start to deviate more and more from the curve.

John: I thought about the ray tracing idea to determine the best angle, too. But what ray are we tracing. From projector, off the strip and back to the center of the audience? But that would be useful only with some sort of gain material where maximum reflectance is angle of incidence = angle of reflection. If that were the right way then you'd be angling the 3 sections illuminated by different projectors differently. No, that's not right. We know it didn't work that way and indeed that method would not minimize cross reflection.

I think I'd start with the idea that the strips are held flat across the stage...the same angle a totally flat screen would be. That would have zero cross reflection but a lot of light is wasted hitting the back of the neighbor strip that is further out. It also wouldn't look right from many seats. From there I'd move on to the idea that each strip is perpendicular to a point in the center of the audience. I think that would give the best illumination and minimal cross reflection.

Posted by Steve Guttag (Member # 268) on 02-10-2003, 09:51 PM:

The gain on a Cinerama screen was about .9 - 1.0. In other words, treat it as matte-white with a very wide scatter. The ribbons prevented the normal washout caused by single sheet screens with such a deep-curve and cross reflection.

Steve

Posted by Mark Gulbrandsen (Member # 72) on 02-10-2003, 10:02 PM:

Steve K.
Indeed there would have to be several plated with differing angles available...all based on the width of the screen to keep them aiming correctly.
Thats why I think a universal plate with adjustable tabs would be best. It would also allow for critical adjustment of the screen as a whole. I just need to see one of the originals to
get some ideas going.
Mark