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Also, inspect your film trap to make sure the pressure pads are clean, as well as the rails. Check the gate alignment, as well as the film lateral guide. It could be pinching your film excessively.

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I had the same sort of problem at a cinema I service on there Scope picture. It was the scope backing lens which caused the problem.It was ok for the first 3 mins then went right out, By shutting the lamphouse douser a touch and limiting the light it focused fine.
A new les cured the problem.

Darren

The reason you are not seeing it so much on scope movies is because flat movies require more of a blowup, due to the smaller surface area of film in the aperture. If this screen has common width masking like most stadium seating theaters have, then this is greatly exaggerated.

As always, we need to know more than the info you have given us. Otherwise we're all just taking stabs at the situation without really knowing the specifics. Post again and this time make sure you tell us:
Make and model of lamphouse
Wattage of xenon bulb in lamphouse
Is there a heat filter between the lamphouse and the projector?
What kind of lenses are you using?
Is this a common height masking setup or a common width masking setup?
Curved screen or flat screen?
Screen brand and surface type (if you know).

That'll help us.

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In addition to what Brad mentioned, the primary lense being used with the scope attachment might be a slower lense. That gives a better focus field. What is the f-stop in the scope primary?

I think the xenon is out of alignment. By the way, what is your Xenon current? Are you over-driving the bulb and it is getting too hot? Also check your stack blower. Without proper xenon venting, things are going to get hotter than hell. If your aperature plate it "too hot to handle", then you definately have a lamphouse associated problem in one area or another.

If there were overheating occurring because of your reflector being mis-aligned, the film would "pop" in the gate and part of the time the center would be in focus, and part of the time it would be out of focus. That could make getting a crisp center difficult (not impossible, but difficult unless the deformation occurred very late in the open shutter cycle).

There should be a pic around here somewhere of a film with heat damage. I'm guessing you would notice it right off if you were having focus problems.

The flat screen rules out curvature problems.

In general, use the lowest gate tension possible that still gives a steady image.

Very short focal length lenses have much shallower depth of focus.

Both Isco and Schneider have done much work in the last 20 years to optimize lens designs to achieve uniform focus across the screen. This work has been recogized by the Academy of Motion Picture Arts and Sciences with multiple awards.

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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
Rochester, New York, 14650-1922 USA
Tel: 585-477-5325 Cell: 716-781-4036 Fax: 585-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion

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