This is topic Running 3-D without selsyn motors in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.


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Posted by Jeff Joseph (Member # 511) on 04-15-2004, 08:33 PM:
 
I'm now running 3-D without selsyn motors... and it works great! I'm posting this so that others know there is a way to do this... and to see if I'm missing something and doing something wrong.

We have 2 V-4's; been running 3-D with selsyn motors, no problem. One motor burned out. Replaced it. Turned out the new motor was faster than the old motor, so had to replace both motors. Now I have 2 new synchronous motors. But we're running them non-synchronous and using the selsyns, no problem.

But now I notice that we're running a little fast, so we switch the motors to synchronous and add some speed controllers. Tweek the controllers so I'm running 24fps... and now I can't use the selsyns. Why? Both speed controllers have to be exactly the same speed... and they're not. Even if both displays say, for example, 57.8, one might be 57.81 and the other one might be 57.82. No way to make them perfectly the same. So the selsyns have to work way too hard and they heat up.

So I call Chapin at Boston Light and Sound. He suggests we run both projectors off one controller (after making sure the controller can indeed handle the current of 2 motors). We install a relay/switch, so when running 2-D, each projector works off one controller. We switch to 3-D, now both projectors work off one controller.

We still have a start switch that turns on both projectors at the exact same moment. So: We set the phase at the same point on both projectors. Then push "start".... both projectors start to run... they stay in sync as they are both seeing the same exact frequency.

And, of course, this would work even if we were not using a speed controller. Both projectors would see the 60 Hz and stay in sync that way.

So: It works. I've run a feature film in double system interlock and it stayed in perfect sync. But it just feels wrong somehow not having the selsyns on.

Am I missing something?

Thanks,

Jeff
 

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Posted by Floyd Justin Newton (Member # 1316) on 04-15-2004, 08:56 PM:
 
Jeff--

What are you missing? You're doing something correctly. Why
worry? It's working!


fjn
Local 294 Ret.
 

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Posted by Richard Fowler (Member # 893) on 04-15-2004, 08:57 PM:
 
No, not missing anything. Selsyn control can be brutal at start up with normal motors, less so with sync motors in their effort to lock in. You have identical sync motors on machines with the same load factors and film passage so the motor "slippage" should be nil under the crystal frequency control of the invertor control....with a normal sync motor with four poles it should have 5 reference points to phase to per film frame.....dissimilar machines would probably be another story.
 

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Posted by Andrew Lee (Member # 1330) on 04-15-2004, 11:29 PM:
 
Jeff, I know that feeling your talking about. Just run with it for the time being. Take a close look at the credits at the very end of your presentation. If they jive.....you're on the way.
 

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Posted by Steve Kraus (Member # 476) on 04-16-2004, 12:16 AM:
 
Eh...a really big timing belt..er...make that a roller chain between machines. SH-1000's would be great for this.

And, of course, this would work even if we were not using a speed controller. Both projectors would see the 60 Hz and stay in sync that way.

Perhaps. But I'd wager there would be a greater chance that the two motors would come up to synchronous speed slightly differently. Remember you'd be throwing them suddenly on 60Hz and they'd not be in sync at first, just trying really hard to get there. With an inverter drive ramping them up from zero they are under full control from the moment you hit start and never given a brief moment to do their own thing.
 

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Posted by Jeff Joseph (Member # 511) on 04-16-2004, 12:29 AM:
 
So most theatres have sync motors nowadays, correct?

At least in those theatres (and that have 2 projectors and can run 6000' loads...and have a silver screen)... all you need to set up for 3-D is a switch to start both projectors at the same time....no need to install selsyns...maybe a few more theatres will set up for double system 3-D.... well, one can hope.

Just as an FYI, as far as I know, there are only 5 theatres in the entire USA currently set up for interlock 3-D:

Castro, San Francisco
Music Box, Chicago
Film Forum, NYC
Lafayette, Suffern NY
Charles Theatre, Baltimore

Jeff
 

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Posted by Pete Naples (Member # 761) on 04-16-2004, 02:52 AM:
 
How well does it work, as surely your two projectors are raked and toe'd in to achieve alignment?

I've installed 2 projector 3D system in the past, these were custom built Balantyne Pro35's with micrometer adjustable lens mounts, which means that the optical centres of both machines were pointing flat and perpendicular to the sheet, the picture alignment being achieve by shifting the lens off axis. Hence nop keystone distortion and hence the 3D works very very well.

Those mechs also have stepper motor drive, via Strongs SV automation, synch'd to SMPTE timcode. The accuracy of synchronisation over a days of showing the same film 4 times and hour is truly astonishing.
 

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Posted by Bill Carter (Member # 156) on 04-16-2004, 04:17 AM:
 
Add the Oak Street Cinema in Minneapolis to your list of interlock and silver screen equipped theaters. They've run the new dual prints of both Kiss Me Kate and House of Wax within the last year or so.
 

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Posted by Steve Guttag (Member # 268) on 04-16-2004, 07:38 AM:
 
Jeff,

Steve is correct...just having sync motors is not sufficient for reliable 3-D operation...the absolutely need to be controlled by the same controller, not hit with a 60Hz line frequency and hope the motor and loading are exact enough to bring them up to speed frame-for-frame.

Are your sync motors 3-phase? That is how the motor controller can really ramp both up at the same time.

It is true that once up to speed, ordinary sync motors driven off of the same line frequency will run turn-for-turn. Anyone that has done interlock know this...they also know that upon start up, film accumulators move a little bit too.

As to your 2-strip 3-D list...

The AFI Theatre at the Kennedy Center in Washington DC is capable and has run many performances. They use the selsyn method.

The AFI/Silver theatre in Silver Spring, MD is a bit more impressive in its ability...in the Historic theatre, they have four projectors. Each pair of projectors can run together and each pair can changeover to the other. The only thing they lack is the silver screen. So they are 3-D ready but not completely done.

The National Archives II in Greenbelt, MD has two systems that are also 3-D capable. The systems were set up for side-by-side viewing of two different prints of the same title but they too are only a silver screen away from 3-D capability.

Steve
 

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Posted by Carl Martin (Member # 1146) on 04-16-2004, 08:02 AM:
 
the castro theater replaced their silver screen (with non-silver) to get more even illumination, so they're not quite there anymore.

a few years ago the stanford theater in palo alto was showing 3-d. don't know if they're still capable.

quote:

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The AFI/Silver theatre in Silver Spring, MD ... The only thing they lack is the silver screen.

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quote: Steve K.

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Just out of curiousity what does it look like if the shutters are not in step?

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quote: Frank said:

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I am not convinced that out-of-sync shutters in a dual projector system would have that much of a negative impact on the presentation.

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Neither am I, since the polarization of the light prevents (under perfect conditions) image crosstalk and since the frequency of the shutters is higher than the persistence-of-vision threshhold.

Quite the opposite, I think it would be easier on the eyes to view out-of-sync shutters because of the reduced amount of light being flashed at once.
 

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Posted by Jeff Joseph (Member # 511) on 04-25-2004, 03:23 PM:
 
Well, we screened a feature on Thursday and guess what? We started the projectors.... and went out of sync. This after doing tests for days, with no problems.

So I rewound, turned on the selsyns, restarted. Ran fine.

Upon reflection and discussion with others, I think the problem was this: Although the projectors stayed in sync once they got going... when we first start, the motors need some extra current... and one of the motors slipped... just enough.

So: We will be running with selsyns in the future; it's not worth taking a chance that the sync will oops.

Jeff
 

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Posted by Pete Apruzzese (Member # 1446) on 04-25-2004, 09:03 PM:
 
Jeff:

Our techs told me when they were setting up our 3-D festival that once the motors are up to speed, I could, if I wanted, turn off the selsyns and everything would stay in sync (our regular 1725 rpm Century motors had been swapped out for 1800 rpm sync motors for the fest as well). I tried it once during my testing phase and it worked, but I wasn't brave enough to try it during a "live" show .

Pete Apruzzese
 

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Posted by Warren Smyth (Member # 1838) on 04-26-2004, 05:04 AM:
 
The National Film Unit of New Zealand produced a three strip wide screen presenation in 35mm for the Osaka Expo in Japan. It later exhibited back here so that the locals could see it.

The three projectors were Toshibas, modified with the addition of selsyns. The three track stereo sound was reproduced with a modified head block on a Westrex double system reproducer, also fitted with a selsyn motor. It had been discovered in Japan that the projector motors ran hot after about ten minutes, so it became standard practice to switch off the selsyns after startup and rely on the induction motors to hold sync. We ran the show every hour, about twelve shows a day for several months without any problems. All four machines held in in frame sync for literally thousands of screenings.
 

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Posted by Paul Cassidy (Member # 951) on 04-26-2004, 05:43 AM:
 
Warren I remember seeing the Roadshow of "This Is New Zealand" at the Embassy Theatre in Auckland and although this was a 70mm cinema they set up the screens in front of the existing one and as I remember this was very impressive presentation at this time ,having 3 separate images to watch and then joining to 1 Huge screen image at times ....... the audience used to stand and clap after each performance
 

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Posted by Warren Smyth (Member # 1838) on 04-26-2004, 08:13 AM:
 
That's the one Paul. It's cost for twenty minutes of screen presentation was $60,000 in 1969. It was never intended to make money as the purpose was to promote the country at the Expo. When the Minister of Trade Jack Marshal saw it in Japan, he insisted that it be shown back here. At a nominal charge it covered it's production costs at the Embassy Theatre in Wellington in six weeks. It then toured and I was one of the projectionists who ran it at Auckland.

In each centre, an additional projection room was built - in our case, in Auckland, in front of the existing one in the circle. The three projectors were located along the front wall of the new projection room so that they sat laterally centred to the optical axis. I think the flat screen was about sixty feet wide. The academy standard aspect ratio was used for each strip with amazing results when the images cut from split screen to a single image across the whole width.

In terms of working, it wasn't unlike three strip Cinerama except all the equipment was housed in the one projection room. With sessions repeated on the hour, we worked much harder though. There was also a fourth projector, an Ernemann which was used to run a twenty minute short on the centre portion of the screen prior to changing over to the three strip presentation. This showed the Expo and some of the technical aspects of the main three strip programme.

It was my first introduction to Xenons. The only technical hitch I remember was a change-over solenoid burning out on one of the Toshiba projectors. As I said, all three projectors and sep mag sound reproducer held in perfect sync with just a start up help from the selsyns.
 

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Posted by Bernie Anderson Jr (Member # 410) on 04-26-2004, 10:24 AM:
 
Out of phase shutters with a 3-D presentation is very annoying. Movement does not look natural, and you get a strobing effect when there is any action. Even lip movement looks wrong.
 

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Posted by Thomas Procyk (Member # 1170) on 04-26-2004, 11:16 AM:
 
It's easy to run 3-D without selsyns...
...just run over/under!

((runs and hides))

=TMP=
 

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Posted by John Pytlak (Member # 331) on 04-26-2004, 11:43 AM:
 

quote: Thomas Procyk

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((runs and hides))

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You can TRY to hide, Thomas, but we'll find you!
 

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