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Topic: Ashcraft 35/70 focusing data

Tim Reed
Better Projection Pays

Posts: 5246
From: Northampton, PA
Registered: Sep 1999

posted 05-28-2004 09:29 AM

The Cinex Special was a very fast lamp that used short 18" positives, as I recall (anything longer would protrude from the front of the lamp and hit the shutter). The working distance was very close.

HOWEVER... another fly in the ointment is that the proper reflector for that lamphouse hasn't been available for 20 years or so (broken master mold?). To get an appreciable amount of light with the replacement mirror, operators were forced to move the positive crater back, precariously close to the contacts. If you run the arc where it was designed to be run in this lamp, the f1 point of the reflector misses the crater entirely. Sad situation.

Just scoot it up against the shutter guard and tweak the crater distance to spread the beam, as I'd venture to say you'll never get it where it should be with that lamp/reflector/projector combination. The reflector(s) you have now (for a Core Lite?) probably will work fine at the shutter guard distance, although the light this lamphouse originally output will never again be realized.

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Kenneth Wuepper
Phenomenal Film Handler

Posts: 1026
From: Saginaw, MI, USA
Registered: Feb 2002

posted 08-31-2004 01:12 PM

Thanks to all for the input.

The Reflector to Aperture plate distance is 35" and the light output is very satisfactory. The entire 35mm frame is evenly iluminated right out to the corners. We have not had a 70mm print in a few years so I have not followed up on that format as yet.

KEN

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Steve Kraus
Film God

Posts: 4094
From: Chicago, IL, USA
Registered: May 2000

posted 08-31-2004 02:42 PM

I wonder if this would provide any useful information: Illuminate the screen as brightly as possible, the most practical way being by running the opposite projector sans film (using a junk lens in case it gets burned); maybe even briefly with the machine stopped if you can get away with it.

With the booth lights out look inside the lamp of the non operating machine and using a white card or tape on the end of the positive and see where the light from the screen is focused into the smallest spot. In theory this should be where the positive is when in operation, give or take a few millimeters on account of depth of crater or corrections needed for uniformity across the screen. Sounds like you are there already but who knows.

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Kenneth Wuepper
Phenomenal Film Handler

Posts: 1026
From: Saginaw, MI, USA
Registered: Feb 2002

posted 08-31-2004 03:25 PM

Steve,

We can illuminate the screen with the three Super Trooper spotlights and then perform your test. I think that is a really "cool" way to get some data. I too wonder how useful that will be.
KEN

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