This is topic Picture staediness in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by Antonio Marcheselli (Member # 373) on 09-24-2001, 02:43 PM:
Hello everyone.Picture staediness of my two Cinemeccanica V5-MI is not very good. At another theater the same projector (Not MI) has a very good staediness.
I wonder what are the common causes of picture instability.
Pls exclude dirty on gate, or incorrect tension on the print.
Few times ago, I exchange maltese sprocket between two projectors and proj. 2 had an incredible improvement in staediness.
Today I've inverted the maltese sprocket on the proj 1 and, it seem, I had an improvement in picture staediness.
I've tried to clean the part of the gates where film is touched (iron in Cinemeccanicas)with Film-Guard, or with something that doesn't allow dirt to fix on it without results.
Do you think that an old maltese sprocket can cause instability?
Or can it be caused by other things?
Thanks for your help!
Bye
Antonio
Posted by John Pytlak (Member # 331) on 09-24-2001, 03:07 PM:
The intermittent and intermittent sprocket definitely will affect vertical steadiness ("jump"), along with the gate tension and friction of the film as it goes through the gate. When the intermittent is in the "dwell" or locked position, there should be no discernable "play" in the pulldown sprocket. Severely worn sprockets can also cause unsteadiness and film perforation damage. Lateral steadiness ("weave") is affected by the edge guiding of the film through the gate, as well as the friction of the film and gate components. The "reference edge" (analog soundtrack side) of the print normally goes against the "fixed guides", pushed into position by spring-loaded "movable guides" or rollers.
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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
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Posted by Rick Long (Member # 213) on 09-24-2001, 05:15 PM:
For a short while back in the 80's, Cinemeccanica put out a VKF version of the 001 sprocket, but these were discontinued for some reason. We found a noticeable improvement in image steadiness with them. Is it possible that one of those machines has this type of sprocket?
The nice thing about Cinemeccanica, of course, is that you can change or invert the sprocket in less than 5 minutes with only a screwdriver.
Posted by Randy Bowden (Member # 587) on 09-24-2001, 06:20 PM:
Try Cranking your intermittent over by hand. This requires removing the belts and turning the drive gear with your fingers. here is what you are looking for. there should be no stiffness at all when the intermittent is in it's dwell position, that is when the cam rides on star. A typical jumpy picture is characterized by one or more stiff spots in the movement. That cam should spin freely when it is not turning over the starwheel. This picture jumpiness problem is quite common among the Bal pro 35 machines, or any other machine with a large star and cam. the only solution is an intermittent rebuild.
Posted by Mark Gulbrandsen (Member # 72) on 09-24-2001, 07:26 PM:
Antonio,
I ahve noticed this problem in the past but on Vic 4's. The problem here is the way they they attach the sprocket t the star shaft. The set screw that holds it onto the end can do two things. It can dostort the sprocket somewhat when you tighten it down, and or it can force the sprocket one way slightly off center of the shaft. This problem is more apparrent on sprockets that have the bore finished a bit too large. Usually loosening and tightening it several different times will help find a happy medium in where it is tightened. If possible also get the sprocket that is manufactured by LaVezzi as it is going to be of much higher quality than the OEM sprocket from Cinemeccannica. Also get the new curved gates as it will make a dramatic difference in picture steadiness and focus.
Mark@ GTS
Posted by Rick Long Jr (Member # 541) on 09-24-2001, 07:50 PM:
Something that I've found that affects picture stability on Cinemeccanica projectors, both Vic-5 and Vic-8's, is the position of the intermittent in its framing travel, as the sprocket moves up or down in relation to the trap. I've found that the image is steadier if you run with the intermittent up closer to the trap. the lower the sprocket is from the gate, the more vertical unsteadiness I usually see. The design has the film leaving the trap is unsupported as it travels to the intermittent sprocket. I've often thought of different ways of installing a Simplex type shoe on a Cinemeccanica to see what would happen.Never tried it yet though. Some of the old reversing Vic-8's I've seen had a double roller arrangement on the intermittent, and they seemed pretty good. Also the new design Vic-5 gate is great, though the plastic levers should be metal as they break easily.
Posted by Josh Jones (Member # 447) on 09-24-2001, 11:59 PM:
Someone also pointed this out on Christie projectors( I think Joe Redifer sp?). the inertia of the film will cause it to continue slidding though the gate even when the movement is in its dwell position. obviously, the more slack there is between the sprocket and the trap, the more inertia, and more jump. It could also be caused by a worn sprocket, grabbing the perf on each frame a little differently, thuse more jump.As far as projectors with large stars, why would this cause more noticeable jump? one would think that this would cause better registration, because of the large parts(assuming they are machined to the same tolerences as other movements), kindof like using a socket set compared to a plyers 
Josh
Posted by Brad Miller (Member # 2) on 09-25-2001, 12:12 PM:
Josh, on the Christies, that is only if the film is overlubricated. Normally that is not a problem and it does take quite a bit of overlubrication to make that happen.
Posted by Josh Jones (Member # 447) on 09-25-2001, 10:26 PM:
Thanks for the info, Brad Josh
Posted by Antonio Marcheselli (Member # 373) on 09-28-2001, 02:26 PM:
Thanks to everyone!I've tried to move the motor knob while keeping in my hand the maltese sprocket ans I didn't felt any movement.
Yes, I can confirm you that now the frame is staedier, after the inversion of the sprocket in the same machine.Mark, I tought too that the lock mechanism of the sprocket could left the sprocket out of center but I tried to move the sprocket without screw and I didn't felt any movement...
Rick, I will try your suggestion.
Bye
antonio