Film-Tech Forum ARCHIVE: Focusing Problems

This is topic Focusing Problems in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Eric Koppen (Member # 2224) on 11-06-2004, 08:20 PM:

Hello,

I am having a focusing problem, and I was hoping you folks could help. I work in a 7 screen theatre, and we run Christie projectors. The problem began at the same time throughout about 4-5 theatres, and in formats Flat and Scope between the theatres. The problem that is happening is that when we go to start the film, it is out of focus. So we adjust it to be in focus, and by the time it gets to the Feature it is out of focus and requires to be focused again.

I believe it is a heat issue, where it goes out of focus when the lens cools inbetween sets, so its focused, then it goes out of focus again when the lens heats up again.

Can someone help me out? If you need more specific info, let me know. Thank you.

Eric

Posted by Gordon McLeod (Member # 33) on 11-06-2004, 09:56 PM:

has your lamps been changed or refocused and the problem developed or is your exhaust fan working

Posted by Ian Joseph Parfrey (Member # 2682) on 11-07-2004, 01:56 AM:

Any emulsion piling up on gate bands?

Posted by Ferdinando Innocenti (Member # 2477) on 11-07-2004, 02:26 AM:

How old is the cinema? Is it the first time it happens? If so, are there any changes in lamps (which brand?) and lamphouse? Have you some kind of electrical motor for focusing (I had a problem once with a switch of a motor)?
Besides, check the temperature of the film. If you need to readjust focus many times, also during the feature, it could be a film deformation, so check every cooling device you had.

Ciao
Nando

Posted by Adam Martin (Member # 641) on 11-07-2004, 01:46 PM:

I also vote for checking the exhaust fan, maybe a loose or broken belt.

Posted by Ian Joseph Parfrey (Member # 2682) on 11-07-2004, 03:29 PM:

Or an incorrectly clamped lens.

Posted by Adam Martin (Member # 641) on 11-07-2004, 04:28 PM:

In 4-5 auditoriums all at the same time?

Posted by Will Kutler (Member # 770) on 11-07-2004, 04:42 PM:

Also check your lenses. If you remove the lenses and gently shake them, do you hear the elements rattling around?

The multi-plex where I worked had all brand new Schneider lenses that apparently came from a bad batch. This problem occured on most of the lenses, and all at the same time. Just about all our lenses had to be sent in for servicing.

Posted by John Pytlak (Member # 331) on 11-07-2004, 08:51 PM:

quote: Eric Koppen
The problem began at the same time throughout about 4-5 theatres, and in formats Flat and Scope between the theatres. The problem that is happening is that when we go to start the film, it is out of focus. So we adjust it to be in focus, and by the time it gets to the Feature it is out of focus and requires to be focused again.

It could be that your pre-show rolling stock ads and trailers have so much "core-set" that they focus differently than the feature. Did you change the way you handle trailers (e.g., winding orientation?). Try winding on larger cores or with a different orientation to "relax" the core-set clockspringing.

Might you be focusing on a snipe that has been treated with a UV-cured protective coating (e.g., PhotoGard)? They may focus differently.

Posted by Randy Stankey (Member # 64) on 11-07-2004, 11:30 PM:

My question is: Does the projector go out of focus gradually or suddenly?

If it happens suddenly, I vote for John P's theory.

Different pieces of film can focus differently. Verify this by standing by the projector and watching the focus. It might seem to suddenly go out of focus.

If it happens gradually, I vote for Will's theory.

The lens(es) could be heating up and expanding, thus throwing the picture out of focus. When the lens cools, it goes back to normal.

Have you changed the xenon lamp(s) recently?

If so, I vote with Gordon and Adam.
Check the alignment/focus of the xenon lamp. It could be out of whack and causing parts of the projector to heat up unevenly. As with the above theory, "heat = expansion = out of focus."

While you're in there, check your cooling & exhaust fans and/or your water circulators to see if they are all working OK.

Just out of curiosity: Do you have Christie lamphouses/consoles with an "Auto Focus" button on them? I've seen more than a few people who change a lamp and think that the "Auto Focus" button automatically aligns the lamp after you change it. In reality, it only moves the lamp's "beamspread" adjustment back and forth when you switch between FLAT and SCOPE films. It has to be recalibrated every time you change a lamp. (Or at least check the calibration.) If this adjustment isn't made or if it's done wrong, it can cause hot spotting which MIGHT cause symptoms you describe. It can also burn your film! Thus, if you have changed lamps recently, this would be a VERY good thing to check into.