What is inside an Optiverter?

[Phillip Grace]

Hi all.
I am looking for detailed information about the Ultravision Optiverter - an optical device which was used to enable two conventional projectors, set up in the booth at 90 degrees to each other, to use a singe projection port on the centre-line of the screen. The light beam from each machine was turned by 45 degrees inside the Optiverter. There has been some discussion here on FT in the past, and there is a picture of it in the SMPTE Projection and Presentation Manual. The device has been described as using prisms to turn the beam, and I would love to see a photo or diagram that shows how they were shaped and arranged. They would also have to be fairly large. I can work out how to do this using mirrors, but wonder if the inventors had come up with a better way.

I would also be interested in getting hold of an original unit, if anyone knows where the bodies are buried.

Cheers.

[Leo Enticknap]

What was the point of this thing? To enable 3-D, to enable changeover projection in a booth that for whatever reason could not have two ports, or something else I haven't thought of? It's an interesting idea, but strikes me as being a solution in search of a problem.

[Randy Stankey]

Apparently, from this link: https://losangelestheatres.blogspot....-theatres.html
(About 1/3 down the page.)

"Wil-Kin's Ultra-Vision projection concept is used in ABC 1 [the smaller house]. Between Century projectors (with Cine-Focus) is Ultra-Vision Optiverter which allows machines to project directly at screen [both from the center port], eliminating horizontal keystoning. Lenses are special design by Kollmorgen."

I guess the idea is that, if your projectors are placed off center of the screen you must deal with horizontal keystoning. Using this "mirror box" allows both machines to project from the center of the screen, eliminating keystoning.

From what I gather, it also required special lenses, as well.

Century-Plaza-1972-Boxoffice-Nov-13-M.jpg

There's a picture but it doesn't seem to show much except that the projectors seem to be sitting at an angle. It doesn't really indicate what this Optiverter might look like. Does it?

[Gordon McLeod]

The idea was that there was no change in keystone of the image when changing over. Glen Bergan developed it for WilKin Theatres

[Phillip Grace]

I think the goal of the Optiverter is to achieve distortion free pictures from dual projectors, particularly on curved screens. It allows both beams to be projected normal to the screen - ie. on both the horizontal and vertical centre lines, instead of from the usual offset positions, several degrees either side of centre. (Perhaps it would be more accurate to say uniform distortion of both images).When this device was around deeply curved screens were very much in fashion. A similar problem exists now when installing dual projectors in a modern auditorium, with relatively short throw and a large screen - even one with a shallow curve. The tolerances are very small. First claim on the centre line goes to the digital projector, with very little space left available either side of it for film projectors and operator.
The Kollmorgen connection is interesting. They certainly made a series of conventional-appearing projection lenses with the Ultravision brand engraved on the barrel. Kollmorgen also made submarine periscopes, with very elaborate optical systems, which raises the question of what else might be inside the Optiverter box such as relay optics and diverter prisms etc.

Another more or less similar system was devised by Trans-Lux for rear-screen projection in their early newsreel theatres. It used a pair of conventional projectors set at an angle to each other directly behind the screen, and lenses with a folded optical system, one left hand and one right hand, not unlike the Buhl RP lenses. This was done to keep both lenses as near to the centre of the screen as possible.