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.

[Mark Ogden]

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.

The Brattle Theatre in Boston is still using the Trans-Lux back projection system. two 45 degree mirrors shoot to another mirror onto a translucent screen. It's not the last word in quality projection, there's hotspotting, but it gets the job done in an awkward set-up in a historic building.



brattle.webp

[Mark Ogden]

Better picture of one, from a 1970 issue of Modern Theater. According to the article, the operator could control everything from the buttons on the back. It puts me in mind of the old TV film island multiplexers, where mirrors would flop up and down to direct the light from two projectors 180 degrees apart to the camera.

I get the idea behind this contraption, but I've been to plenty of theaters with deeply curved screens and have never really been bothered by keystoning. The Cinerama Dome got by without one, and the Uptown, and the Cooper, et.al. The article, written by the aforementioned Mr. Berggren (with a LOT of exclamation points), speaks of a "motorized lens mount" and says that each changeover occurs with a "neat fade-in and fade-out". That would probably annoy me more than keystoning.

optiverter.jpg

[Ryan Gallagher]

I tried to reply here but mis fired it into another thread the other day:

Yeah I wish our systems could better share center (or not need to). This is the crevice only skinny techs can access for certain service tasks on eiither. (Film No.1 is on center)

IMG_6646.jpg

[Josh Jones]

I tried to reply here but mis fired it into another thread the other day:

I was wondering what the hell you were talking about

[Tj Hopland]

In the reply 7 photo what's going on in the penthouse area? Those are not the JJ penthouse. It could be the Tommy Song Remains The same era so 4 track? But they don't look like any of the 4 track penthouses either. Century did have their 6-4-1 sound system where the preamps were up there behind the magazine but that ain't it. What ever that box is does look like its got the Century logo on it but the conduits don't appear to go to the penthouse thing. Box on the wall to the right also with a Century logo is likely the power amp, likely a green Altec or two in there sitting on their side in little racks.

There is that horizontal(ish) conduit at the top of the projector head, I remember seeing Cinefocus machines where the inlet was there vs on the front but I don't see the blower, that usually sat on the floor or is it there mounted to the front of the base? Kinda tucked in there where the neck extends out? You can see a round shape there with a lighter color dot in the middle, perhaps the cap on the motor bearing? So is the penthouse thing maybe part of the fade change over thing? Can't tell if that is a standard 'Zipper' where that hose bends over the shutter or not. Some kind of automation cue reader sort of thing? Some sort of film cleaner? Those square boxy bits is whats got me, too small and not round to be flywheels if it was a soundhead so that's why I'm thinking some sort of automation or cleaning thing.

In what documentation there is on this system is there any sorts of clues to what the room and screen dimensions were? Were these fairly short ratios? Remember back then something like a 4:1 was pretty typical. Were these maybe some sort of 'extreme' like a 2:1 and that is why the change over distortion was worth trying to fix? It would not be all up to just the throw ratio I would think all the other ratios would come into play as to how noticeable it was. Wall to wall screens didn't tend to be a thing so if that was something they were trying?

[Gordon McLeod]

Those are Ampex penthouses on SA or DA projectors

[Mark Gulbrandsen]

Not 100% sure, but that may have been the only Optiverter ever installed... Same picture and article was Featured in International Projectionist back in the day. The fade in and out to the other machine would have killed it off really fast.
Those are very definitely Ampex penthouses. I have run into several of them sitting on shelves in theaters, plus Lee Artoe used to have a bunch of them in his building in Chicago. They are made of cast iron... Go figure that Ampex would do something that stupid.

[Ryan Gallagher]

I expect it was a novel approach for extremely short throws or curved screens where off center keystone is exaggerated. Rear projection as mentioned earlier is typically in the extremely short throw territory too.

[Gordon McLeod]

the Translux system was based on the rear projection systems used on many of the grand cruise liners back in the day. In a translux booth the machines actually did not directly face each other but were angled and they did not use exposed mirrors but had a lens with the mirror built in many of them were made by Buhl optical

[Jim Cassedy]

The Brattle Theatre in Boston is still using the Trans-Lux back projection
system. two 45 degree mirrors shoot to another mirror onto a translucent screen.

Thanks for that picture of the TransLux rear-screen device. I know I had a good picture of one
somewhere here on one of my old laptops, but I can't seem to find it anywhere. The original
TransLux theatres were smaller venues, sometimes operating in spaces that had been vacant
store fronts, and used a rear projection system and a special translucent screen that allowed
them to keep the house lights up slightly. They were very popular during WWII, when many of
them ran newsreels and shorts 24/7. In most cities, there was a union projectionist in the booth
(which was behind the screen) but the front-of-house was often staffed by only one or two
people who sold tickets and sold concessions, etc, like most 'neighborhood' cinemas in
smaller communities do today. In the 1960's, I know TransLux also operated several full
size theaters in NY and perhaps other cities.

Anyone who has worked in television has had experience with the optical multiplexer device
which was part of the 'film chain', which front surface mirrors or sometimes a prism which
allowed multiple movie and/or slide projectors to work using only one (expensive!) TV camera.

TransLux bought the rear-screen patent rights from a guy named Lester Bowen who had
designed it back in the 1930's. Bowen's device used a pair of angled front surface mirrors
which moved up and down vertically using a solenoid to switch between two 35mm projectors
and bounce the image onto translucent screen. A later patent revision changed the two vertical
mirror system to a single mirror that swung into position, like most TV film chains later used.

TransLuxPatPic.jpg

(Note that they were using carbon arcs: "the way things should be" -jc- )

A bit somewhat unrelated, but in the big screening room here at Dolby's HQ here in San Francisco,
we used right-angle device keep the lens of a large Christie 4K projector on more or less the same
'optical center' relative to the screen as the their two DolbyVision™ projectors. As you can see
in this photo, the Christie is mounted 90° from the DV projectorthingys and screen.
DolbyChristie_1.jpg

Closer View
DolbyChristie2.jpg
The Christie was there mainly as 'back-up' in case the DV system failed for some reason, or was used to put
computer graphics or sponsor slides, etc on screen before some premiere or film festival screenings held there.