Film-Tech Forum ARCHIVE: Gate Tension

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Topic: Gate Tension

Brent Arnold
Film Handler

Posts: 20
From: Grapevine, TX, USA
Registered: Feb 2002

posted 07-03-2002 04:46 PM

My image seems to be going back and forth (from the right to left and back) and I was wondering if this is a problem with the gate tension. I realize that it is a problem with static, probably, but I am wondering if adjusting the gate tension will help. And if it will how do I fix it (By the way I have an old century projector... not sure what year, but it is old)

Thank You.

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Brad Miller
Administrator

Posts: 17775
From: Plano, TX (36.2 miles NW of Rockwall)
Registered: May 99

posted 07-03-2002 04:50 PM

Static has nothing to do with it. Gate tension for the most part does not either. (Too much can aggravate it.) Your problem is with the lateral guide roller right by the framing window. The soundtrack edge roller should not move, whereas the picture edge roller SHOULD have a spring action. Overall they need to spin freely as well. Is this a problem with one particular print? If so, which one? Check that and report back.

Do note that if the roller is improperly adjusted you can cause the image to be off center or you could end up showing the edge of the film on the screen. You could also make the problem worse. If you've never adjusted this before, you are best off letting your tech come in and show you how to do it.

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Scott Norwood
Film God

Posts: 8146
From: Boston, MA. USA (1774.21 miles northeast of Dallas)
Registered: Jun 99

posted 07-03-2002 05:50 PM

For the sake of completeness, I'll explain how the gate tension adjustment works on Centurys, although, like Brad said, this won't help the problem described.

Newer 35mm Centurys have flexible bands in the film trap; the gate presses the film against these bands and tension is set by adjusting the tension of the bands. This is set using a smallish knob (usually with a numbered scale) at the top of the trap. This is very similar to the same adjustment on a Simplex X-L or PR1014.

Older Centurys (Cs and early SAs) don't have the flexible bands, but instead have _two_ adjustments on the gate itself, one each at the top and bottom of the gate.

Older JJs don't have flexible bands either; the tension adjustment is a knob on the gate, to the left of the large knob that one uses to open the gate. This is the same location as the thumbscrew in 35mm Centurys that one unscrews to remove the gate for cleaning.

I don't know about newer JJs; maybe someone else does.

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Paul G. Thompson
The Weenie Man

Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000

posted 07-03-2002 05:53 PM

Check your lateral guide roller in the top of the gate assy. It might be sticking or just out of adjustment. A good cleaning may correct your problem.

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 07-04-2002 07:53 AM

Pull out the apperture and looke at the projected image of the perfs
That will tell you quickly if it is the print or the machine If the perf edges are steady it isn't the machine

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Daryl C. W. O'Shea
Film God

Posts: 3977
From: Midland Ontario Canada (where Panavision & IMAX lenses come from)
Registered: Jun 2002

posted 07-05-2002 03:21 AM

If you can't see the perfs when you pull out the apperture (the best way to tell), check to see if your trailers and rolling stock are steady or moving around. If these are steady then it's probably the print and not the machine.

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 07-05-2002 06:49 AM

Don't trust trailors or rolling stock as they could have defects as well. Use the perf or SMPTE 35PA
Just pull the plate

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

posted 07-09-2002 01:06 PM

I agree that the best "test" of projector steadiness is to pull the aperture so you can see the edges of the print perforations (usually along the far right side of the projected image). If the actual perforations on the print are "rock steady", your projector is doing its job in projecting a steady image.

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
Rochester, New York, 14650-1922 USA
Tel: +1 585 477 5325 Cell: +1 585 781 4036 Fax: +1 585 722 7243
e-mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion

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Daryl C. W. O'Shea
Film God

Posts: 3977
From: Midland Ontario Canada (where Panavision & IMAX lenses come from)
Registered: Jun 2002

posted 07-10-2002 12:07 AM

I totally agree that pulling the plate is the best thing to do. However if you are unfortunate enough to have top masking it can be often difficult to make out the perfs on the masking even with all the lights off in the theatre. It becomes especially difficult if the perfs are projected into the corner of the wall.

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

posted 07-10-2002 09:11 AM

If you can't shift the projector/masking to project the perfs on the regular screen, set up a portable "screen" (e.g., large piece of cardboard) close to the projector and focus on it to observe any movement of the perfs.

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Mike Jones
Expert Film Handler

Posts: 108
From: Birmingham, MI, USA
Registered: Jul 2000

posted 07-12-2002 12:08 PM

I agree with the weenie man, probably a sticky lateral guide roller. those other metal guides usually don't move, and therefore probably don't need adjustment. but, give it a look.

word,

Mike

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Wes Hughes
Expert Film Handler

Posts: 175
From: Raleigh, NC, USA
Registered: Aug 2001

posted 07-13-2002 10:56 PM

I would check for worn or improperly adjusted studio guides.

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