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This topic comprises 2 pages: 1 2
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Topic: Achieving uniform focus
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Steve Guttag
We forgot the crackers Gromit!!!
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Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
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posted 05-12-2004 08:39 AM
Matt,
You don't run across that many screening rooms...obviously. I have literally 100s of PC adapters out there. The ONLY place I've installed with turrets are for main-stream cinema. Most the screening rooms I deal with have 4-5 lenses per machine (1.85, 1.66, 1.37, Scope, Silent and then there may be one or two lenses for 16mm). Turrets don't exactly work there.
We just installed PC adapters in Ambler, PA to deal with some extreme keystone issues as well.
The PC adapter gives the experienced tech a lot of control over the picture placement and appearance. ISCO's will shift as much as 5mm in any direction...Schneider's new one will shift a lot more but it is more pricey. However, when dealing with Silent/super-35 or with long focal length lenses they are quite valuable tools.
However, with that being said...in the typical Flat/Scope theatre, they are rarely necessary.
Steve
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Frank Angel
Film God
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Posts: 5305
From: Brooklyn NY USA
Registered: Dec 1999
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posted 05-12-2004 08:48 AM
In the old Brandt theatres on Forty-Douch Street in Manhattan, most of them, like the Victory, the Amsterdam, etc. had booths sitting up 5 and 6 stories above the stage and with very short throws. The angle was insane. All these theatres had fly-hung screen frames on the first or second pipe of the stage (they originally all did vaudeville stage shows along with films, and hence they were designed very shallow so actors' voices would carry to the back of the theatre). The solution all those theatres used to deal with severe keystoning was to simply grab the bottom of the screen and pull the sucker downstage as much as needed to get it fairly close to being parallel to the projector lens. The keystoning would have been terrible without doing that. It didn't correct keystone distortion completely (the damn screen would have had to be laying practically flat on the stage for that), but it was reduced enough to become livable. And that tilt in the screen, from a young audience member like me, looked kinda cool. Sort of reminiscent of the CinemaScope curve, which it turns out, some of those old houses still maintained WITH the tilt.
In my theatre, the booth is 5 stories up, but the throw is much longer (I think about 120ft) so that minimizes the keystoning error, but we still needed to get a hold of special brackets for the take-up magazines which thrust the magazine forward so it does not hit the pedestal. Without it, you can't get the angle you need without crushing the magazine against the pedestal base as you crank the tilt adjustment wheel. I also had to get a roller from Kelmar to push the take-up belt so it didn't rub against the Simplex soundhead casing.
Interstingly, we tilt the screen DOWN toward the middle of the orchestra, not up toward the booth (which, in fact, INCREASES the keystone error). We do this simply because we need as much light as possible to be reflected back to the center of the orchestra, NOT back up to the top of the balcony. We can live with the keystoning which is properly masked away by the aperture plate and the masking, but we can't loose all that light to the heavens. Living with some keystone distortion in the image geometry (but still maintaining a perfectly rectangular looking screen) is the much lesser of two evils.
Of course none of this screen tilting chicanery will work on anything but matte screens surfaces. Any gain screen will cause light to fall off at the bottom if you are tilting it up to the booth, especially in the magnitude of tilt that the Brandt theatres were using.
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