8mm Forum: Unstable image

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Posted by Rob Koeling (Member # 35) on July 09, 2007, 08:24 AM:

I've got this problem with a Bauer T510 projector (but I suspect that the fault could happen on other projectors too).

The thing is that the image becomes unstable when I move the framer in one direction. If the frame is all the way down, the image is perfectly stable (but the framing is not perfect; you can't see the whole frame and part of the following frame). When I move the framer, the image becomes unstable. The image becomes more and more jittery the more I adjust the framer. Does anyone have any ideas about what might cause this?

Any thoughts are appreciated.

- Rob

Posted by John Whittle (Member # 22) on July 09, 2007, 08:51 AM:

Well, there are two basic ways of "framing" the picture.

1. The actual mask is slide and the picture moves up or down physically and you have to re-level the picture. In this case you shouldn't see any jitter once the plate is stable.

2. Optical centering. The fulcum of the claw lever is moved up and down and the mask stays in position. Once the projector has been aimed at the screen (without film) the framing lever adjustment will then optically center the picture. This is a more complicated method and requires more parts.

If the problem is with the first, it might just be some lubrication is necessary. A light rub of bees wax on the gate plates might solve it.

If the problem is with the second, it could be worn parts, loose parts, or mis-adjustment of the fulcum such that the pitch angle or claw protrustion is changing and hitting the edge of the perforation as well. This would make the projector much noisier when the picture was jumping.

Maybe this will help you look for the cause. Post your results.

John

Posted by Ugo Grassi (Member # 139) on July 09, 2007, 04:59 PM:

1)to remove the bracket with the pressure plate.
2)to move the framer in the direction where you note the problem
3) To put (by hand) a piece of film into the film path to engage the perforation to the pins
4) to move the main tree knob to observe the pin-claw movement

If the pins touch the lateral side of the perforation, it means the claw is out of right position.

Posted by Paul Adsett (Member # 25) on July 09, 2007, 05:10 PM:

The solution to this problem is usually to adjust the position of the fixed side edge plate in the gate, so that the claw is engaging the exact center of the film sprocket holes. This should take care of the problem. It's a very easy adjustment to carry out, usually with some trial and error. Adjust the framing to the nominal center position first, and then when you have the side plate in the correct position you should be able to adjust the framing over its full range without getting any film chatter.

Posted by Ugo Grassi (Member # 139) on July 10, 2007, 12:39 AM:

quote:
The solution to this problem is usually to adjust the position of the fixed side edge plate in the gate, so that the claw is engaging the exact center of the film sprocket holes.

This is a solution, but I don't like it. At first, in the Bauer machines that part is fixed, so you cannot move it.
In the machine where it's mobile (there are some screws), when you move it, you loose the right frame position respect to the little picture in the film path.
I may note this "out allignment" in many projectors by the SMPTE film test

Posted by Graham Ritchie (Member # 559) on July 10, 2007, 03:41 AM:

Rob
When you say unstable image, are we talking about vertical or horizontal movement, if its side then what Paul has mentioned would be a good place to start. I would sit a bit of scrap film in the gate and manually and slowly move the projector and observe with a magnifying glass your claw engagement and pull down of the film. If its vertical and gets worse as the framing knob is moved then it sounds like your top loop is to small, try to centre your framing before threading, eg counting the total turns and then set it mid-way, other than that I would try giving the film a clean and lube and see what happens, most times a juddery vertical image is the film itself.

Graham.

Posted by Rob Koeling (Member # 35) on July 10, 2007, 04:19 AM:

Thanks for the replies guys!

I should have mentioned it is vertical movement. It does quite considerably worse when I move the lever, but it doesn't seem to be the case that the upper loop is too small (it does get smaller, of course). It seems to me that Ugo is on the right track for my case. I'll get the machine out this afternoon and do the test that he suggests. The projector does get very noisy. It sounds like the claw is not alligned with the sprockets properly and touches the film at each movement. I'll perform Ugo's test and confirm later.

If this is the case, are there any thoughts on re-alligning the claw?

Thanks!

- Rob

Posted by John Whittle (Member # 22) on July 10, 2007, 09:36 AM:

quote:
If this is the case, are there any thoughts on re-alligning the claw?

Be very careful! On some projectors there are screws which allow movement of the claw arm and thus it's position and pitch. On others, the claw has an area which is bent ("form to spec") such as some Bell & Howells. For those machines there is a tool which allows you to grasp the proper part and apply pressure.

Make sure you've identified the problem properly before you make any adjustment. If in doubt, find someone with a service manual for your projector.

John

Posted by Martyn Stevens (Member # 861) on July 10, 2007, 11:21 AM:

Rob,
This isn't happening with just one film, is it? I've met the same problem and it's usually when I have to push to the limits to get the racking right. It's not unknown for s film to be printed out of rack enough to do this.

Martyn Stevens

Posted by John Whittle (Member # 22) on July 10, 2007, 03:26 PM:

quote:
Thanks for comment on LED as exciter. I don't really know enough to fully understand, but let me try this question. On the Pathe Vox/Super Vox, the scanning beam is produced by an adjustable slit in the sound telescope - I have adjusted these to get better "top". Would an LED work for this set-up?

It's also not unusual to find one film that is either green (although most of our films are many years out from the lab--but it was a constant problem for me back in the 70s) or been treated with something that's "gone sticky". This will also exhibit similar problems with noise and unstable picture and might only be happy in a "sweet spot" that's out of frame.

If the print is from a 16mm camera original, the frame lines varied widely, if it's from 35mm and out then it's probably reduction printed one full perf off of the frame line--a lab reject and should have been replaced with the old negative destroyed.

John

Posted by Rob Koeling (Member # 35) on July 10, 2007, 03:29 PM:

Ugo,

Can you tell me how to remove the bracket with the pressure plate?
It's not immediately clear how to take it out....

Martyn, no it's consistent with any old print.
John, thanks for the warning. When it comes down to bending, I'm gonna send the machine of to someone who has done this before!

Thanks,

- Rob

Posted by Ugo Grassi (Member # 139) on July 12, 2007, 01:22 AM:

You have to remove the front lid. Then turn the main knob until the reverse position. Done? Well, now don't stop to turn the knob because there is a last "secret" position that's able to unlock the bracket.

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