This is topic Aperature problems? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.


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Posted by Mike Lauber (Member # 1486) on 02-09-2003, 01:50 PM:
 
Hello there. A couple of the screens at my theatre are beginning to have problems where the picture doesn't fill the entire screen or spills over onto the curtains. Some fill it perfectly vertically, but don't fill it horizontally. Some don't fill it properly vertically. Also, on some screens it will fill the screen just fine with a scope lens/aperature, but not with flat, or vice versa. The curtains stop in a fixed location in each theatre for flat and scope films, so I doubt they are the problem. These problems are too small for most people to notice presently, but I would like to correct the problems before they get worse. How can I fix these problems?

Mike
 

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Posted by Paul G. Thompson (Member # 655) on 02-09-2003, 02:20 PM:
 
If the apertures were cut properly from day one, there are other factors that need to be looked at such as is the floor sagging, is the projector moving about the projection booth, is your masking rigging set properly, is your lamp properly aligned, and is the lens holders in the projectors worn out allowing the lens to flop around? These are just a few, but not all, things to look at.

Edit...Tim, does that look better?

Making new apertures will not solve your problem until you find out "what is changing" in your enviroment.

[ 02-09-2003, 07:19 PM: Message edited by: Paul G. Thompson ]
 

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Posted by Tim Reed (Member # 137) on 02-09-2003, 03:24 PM:
 
Hi, Mike! Paul is right, you should look to find out what has changed. Make sure no one has swapped aperture plates from one house to another - that's fairly common. Also, make sure the same lenses are being used in the same projectors everytime. And, if you have turrets, the adjustments on them can slip and cause the lens to shift from the ideal position. Any of these conditions can cause over spill or aperture edges to show on the screen.

Since we were just talking about spelling on another post, and as a point in fact, please note they're apertures, not aperatures.

Paul, you should know better - start banging those erasers.

Mr. Reed, 3rd period English teacher
 

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Posted by Mike Lauber (Member # 1486) on 02-09-2003, 05:12 PM:
 
I don't believe it's the projectors moving, because on most of them, the picture is still fine vertically, and too narrow on BOTH sides of the screen, so it couldn't have just shifted one way or the other. What exactly is the masking on the projectors? How do I adjust it? Is it possible for the aperture plate to become slightly warped? I've been thinking of simply filing down the aperture plates.

Mike
 

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Posted by Brad Miller (Member # 2) on 02-09-2003, 05:27 PM:
 
Mike, when you go from flat to scope, does the side curtains open, or does the top masking come down from the ceiling? Do you have masking motors, or do you go down into the auditorium and pull a rope on a pulley?

I have seen rope stretch as well as the set stop points on masking motors drift. Still, *most* of the time it is turret related. It would also help to know what kind of projectors you are running, and if you have turrets or if you swap the lenses out to change formats.
 

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Posted by Mike Lauber (Member # 1486) on 02-09-2003, 05:42 PM:
 
We pull curtains on the sides. Rope streching is one strong possibility I suppose. We do not have turrets on any of our projectors. I change the lenses manually. I'm about to go to work right now, so I'll check exactly which projectors are having problems and post again later. Thanks.

Mike
 

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Posted by Scott Norwood (Member # 30) on 02-09-2003, 06:28 PM:
 
I'm betting that someone accidentally swapped aperture plates between projectors or is doing something like using Academy plates for scope prints. (scope plates are taller than Academy plates)

Is this theatre a newly constructed house (built in the last few years) or an older theatre? With new installations, it seems fairly common for the building and masking to "settle" over the first few years and that may be part of what you are seeing as well.
 

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Posted by Paul G. Thompson (Member # 655) on 02-09-2003, 06:49 PM:
 
Tim, I blame the keyboard. So, "Pbpthbpthbthp!"

Tim, I tried to use "white-out" on the monitor...but that didn't work....
 

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Posted by Tim Reed (Member # 137) on 02-09-2003, 09:22 PM:
 
Ummm-hum. When all else fails... blame the equipment!
 

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Posted by Paul G. Thompson (Member # 655) on 02-09-2003, 10:24 PM:
 
Well, it works when you blame the dog...
 

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Posted by Rick Long (Member # 213) on 02-09-2003, 10:42 PM:
 
"The curtains stop in a fixed location in each theatre for flat and scope films, so I doubt they are the problem." How do you know they are still stopping at the same place as when the apertures were first filed? Ropes can strech, and limit switches can drift due to mechanical wear.

They worked well once. Last thing I would touch is an aperture file and NEVER without RP-40.
 

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Posted by Paul G. Thompson (Member # 655) on 02-10-2003, 01:41 AM:
 
Jeeze, Rick. I thought I read WD-40 instead RP-40. I guess I fit the typical projectionist...Blind in one eye and can't see out the other..
 

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Posted by John Pytlak (Member # 331) on 02-10-2003, 09:08 AM:
 
You can order test films directly from the SMPTE. Theatre equipment dealers often carry them in stock too, and may sell short lengths of 35-PA for loops to verify projected image area (Never use a loop of 35-PA for anything else, like evaluation of resolution or steadiness --- only a full length in good condition should be used for that.)

http://www.smpte.org/smpte_store/test_materials/

I agree the most likely cause was that someone switched plates among theatres, or the screen masking stops got out of adjustment. If the theatres were set up properly in the first place, there should be NO need to file apertures.
 

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Posted by Paul G. Thompson (Member # 655) on 02-10-2003, 02:21 PM:
 
John said:

quote:

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I agree the most likely cause was that someone switched plates among theatres, or the screen masking stops got out of adjustment. If the theatres were set up properly in the first place, there should be NO need to file apertures.

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