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Author
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Topic: Sproketless Projectors
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Paul Adsett
Film God
Posts: 5003
From: USA
Registered: Jun 2003
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posted May 01, 2019 11:20 AM
The only sprocketless projector I have is the Eumig 926GL Stereo. Actually it does have a rear sprocket, but the all important feed sprocket, which isolates the feed spool tug, is absent, being replaced by a tiny flapper roller on a thin metal beam spring ![[Roll Eyes]](rolleyes.gif) . This works fine with a rock steady picture up until the last few minutes of any reel, when the claw is tugging the supply film reel close to the center hub of the reel and the jerking force on the reel is much higher. This produces film unsteadiness and sometimes 'free running' of the film over that last couple of minutes. I have tried increasing the gate clamping force by stretching the gate springs a little, and that helps a bit but does not totally solve the problem, the root cause of which is the lack of a feed sprocket.
So my questions are this, are all sprocketless projectors subject to this problem of unsteady pictures at the end of the reels? And what are the advantages (if any) of no feed sprocket?
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The best of all worlds- 8mm, super 8mm, 9.5mm, and HD Digital Projection,
Elmo GS1200 f1.0 2-blade
Eumig S938 Stereo f1.0 Ektar
Panasonic PT-AE4000U digital pj
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Paul Adsett
Film God
Posts: 5003
From: USA
Registered: Jun 2003
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posted May 01, 2019 05:37 PM
Maurice, the two rollers that I installed on the top of the S926GL are very helpful in dampening the wild thrashing mode of the film coming off the supply reel, but unfortunately this still does not isolate the film tension load from the claw, so the film still tends to jump or skate through the gate towards the end of the reel.
And that's the bad thing about sproketless projector design- the behavior of the film is dependent on so many variables, spool hub diameter, friction coefficient of the film and gate, spring loading of the gate, flexibility of the film base etc. So some reels will run fine with no problems and others will be very unhappy towards the end of the reel.
All of which raises the question why would anybody(particularly 'The Wizard's of Vienna') design a sproketless projector in the first place?
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The best of all worlds- 8mm, super 8mm, 9.5mm, and HD Digital Projection,
Elmo GS1200 f1.0 2-blade
Eumig S938 Stereo f1.0 Ektar
Panasonic PT-AE4000U digital pj
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Paul Adsett
Film God
Posts: 5003
From: USA
Registered: Jun 2003
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posted May 02, 2019 05:34 PM
To Maurice's point: yes the film coming off the supply spool of the 926 is essentially reversed in direction (180 degrees) when entering the feed slot at the top of the projector. In addition to that the film also has to be displaced sideways because of that coaxial reel arrangement. This is all accomplished before the film enters the gate by a molded plastic piece with 3 tiny rollers and a flapping roller on a metal beam spring, to help absorb the tug of the film on the claw. Its all a very complex and tortuous film path and a real nightmare for the film, although in all fairness, as bad as this design is, amazingly I have never scratched any film on my 926. So Eumig did a great job on a rotten design concept! ![[Big Grin]](biggrin.gif)
But all this complexity just to make a projector look novel and different from the competition was a very bad decision indeed. I am sure there were engineers at Eumig ( particularly those who had designed the prior superb 800 series projectors) who hated this coaxial single sprocket design, and surely knew of its peculiarities and fussy operation, but were in all likelihood overruled by the demands of the marketeer's and bean counters.
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The best of all worlds- 8mm, super 8mm, 9.5mm, and HD Digital Projection,
Elmo GS1200 f1.0 2-blade
Eumig S938 Stereo f1.0 Ektar
Panasonic PT-AE4000U digital pj
| IP: Logged
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