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Author Topic: Running 3-D without selsyn motors Pete Naples Phenomenal Film Handler Posts: 1565 From: Dunfermline, Scotland Registered: Feb 2001 posted 04-16-2004 01:10 PM                     John, the sync on those Ballantynes I worked on in Spain was quite astounding, you'd stand behind then as the ramped up and down and you'd see that both shutters were turning in perfect sync! As described by Gord, those machine are driven by DC stepper motors, and each machine has a shaft encoder. I'm still interested as to how good the effect is with 'normal' alignment of the pictures?  |  IP: Logged Jeff Joseph Expert Film Handler Posts: 131 From: Palmdale, CA, USA Registered: Jun 2000 posted 04-16-2004 01:26 PM                        Gordon: We do have the speed controller set to take 3 seconds to ramp up to speed, which seems to work fine. I guess since we have selsyns anyway I can turn them on, but it seems redundant. Is it?  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 04-16-2004 01:37 PM                     Selsyns on sync motors is a bad idea. You would have two things (sync motor and selsyn motor) fighting to win a battle and neither wants to loose. Steve [ 04-16-2004, 05:10 PM: Message edited by: Steve Guttag ]  |  IP: Logged John Anastasio Master Film Handler Posts: 325 From: Trenton, NJ, USA Registered: Sep 2000 posted 04-16-2004 02:06 PM                        If you're just running synchronous motors on one controller, then there's no way to adjust the shutter timing on the run. It was done with an optical device originally, with the projectionist viewing slots or holes cut into each shutter to keep them aligned by looking at the screen through a rotating polarized set of filters running in synch with the selsyns. Even if you could get one running along with the projector motors, there'd still be no way to make adjustments, short of carefully applied brute force braking on one machine. If your machines are stable enough to stay timed the way you're running them, I'd say go with it, though. Why argue with success?  |  IP: Logged Jeff Joseph Expert Film Handler Posts: 131 From: Palmdale, CA, USA Registered: Jun 2000 posted 04-16-2004 04:11 PM                        It's tough to adjust phasing in any event. That's why you should be in phase and "locked" before you start your show. Jeff  |  IP: Logged Steve Kraus Film God Posts: 4094 From: Chicago, IL, USA Registered: May 2000 posted 04-16-2004 06:35 PM                    Just out of curiousity what does it look like if the shutters are not in step?  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 04-16-2004 08:27 PM                     eye strain and headache is the result I do all my 3d stuff nowdays with servo DC motors aith a shaftencoder or steppers  |  IP: Logged Adam Martin I'm not even gonna point out the irony. Posts: 3686 From: Dallas, TX Registered: Nov 2000 posted 04-16-2004 08:55 PM                     quote: Steve K. Just out of curiousity what does it look like if the shutters are not in step? Imax GT projectors run with the left eye 1/4 frame ahead of the right eye. The left eye is being projected while the shutter is closed on the right eye, etc. The SR projectors (dual projector system) runs with both projectors in shutter sync.  |  IP: Logged Jack Ondracek Film God Posts: 2348 From: Port Orchard, WA, USA Registered: Oct 2002 posted 04-16-2004 11:13 PM                        I'd be more interested to know how you got 2 Ballantynes to put out a stable enough picture to pull off 3D in the first place!  |  IP: Logged Pete Naples Phenomenal Film Handler Posts: 1565 From: Dunfermline, Scotland Registered: Feb 2001 posted 04-17-2004 05:09 AM                     Picture stability? Wasn't a problem. Maybe SV Mechs are different to standard? I don't have a lot of experience with Balantyne Pro 35 outside of SV work, I've never seen one in a normal cinema, they are fairly popular in Europe for for SV application, both in 35mm and 70mm, both 5 and 8 perf.  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 04-17-2004 05:13 AM                        We are also a silver screen away from a viable dual projector/polaroid 3D system. The selsyns are ready but it just doesn't look like the screen will ever happen. As for out-of-sync shutters, doesn't the IMAX shutter glasses system work entirely on the principle of alternate projection of one eye then the other? Isn't that pretty much exactly what out-of-phase shutters in a dual projection system will look like to the viewer? I watched quite a number of IMAX 3D shutter glasses presentations and never seemed to be bothered by the fact that neither eye was ever "on" at the same time. In fact, the 3DTV home video system uses the alternate frame/shutter glasses as well and it works very well indeed. 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. There's a neat experiment -- Jeff, you are in a position where you could easily run a real with shutters in perfect sync and then again witht them purposely timed out of sync. You have the makings of a sweet little SMPTE white paper submission. Just tell us your findings first.  |  IP: Logged Adam Martin I'm not even gonna point out the irony. Posts: 3686 From: Dallas, TX Registered: Nov 2000 posted 04-17-2004 05:20 AM                     Actually, the Imax GT projector can work with polarized glasses *or* the electronic LCD shutter/polarized hybrid glasses. The LCD shutter in the hybrid glasses completely blocks out the opposite-eye image, greatly reducing the crosstalk (ghosting) between the eyes by working in time with the projector's shutters. quote: Frank said: 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. 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.  |  IP: Logged Jeff Joseph Expert Film Handler Posts: 131 From: Palmdale, CA, USA Registered: Jun 2000 posted 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  |  IP: Logged Pete Apruzzese Film Handler Posts: 13 From: Mountain Lakes, NJ, USA Registered: Sep 2002 posted 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  |  IP: Logged Warren Smyth Expert Film Handler Posts: 158 From: Auckland ,New Zealand Registered: Aug 2003 posted 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.  |  IP: Logged

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