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» Film-Tech Forum   » Operations   » Film Handlers' Forum   » How to determine distance between lamp and gate?

Author Topic: How to determine distance between lamp and gate?
Gary Wachter
Film Handler

Posts: 21
From: Coppell, TX, USA
Registered: Jul 2010

 - posted 03-29-2019 05:54 PM      Profile for Gary Wachter   Email Gary Wachter   Send New Private Message       Edit/Delete Post 
There have been plenty of discussions on aligning the optical axis, but little on the proper distance from the light source to the film. How would this be determined?

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Matthew Ortado
Film Handler

Posts: 20
From: Halethorpe, MD, USA
Registered: Jan 2010

 - posted 03-29-2019 07:56 PM      Profile for Matthew Ortado   Email Matthew Ortado   Send New Private Message       Edit/Delete Post 
Each lamphouse has a specific working distance. You would have to look at the manual, it is listed there.

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Lindsay Morris
Expert Film Handler

Posts: 232
From: Darlington, WA, Australia
Registered: Sep 2002

 - posted 03-30-2019 06:27 PM      Profile for Lindsay Morris   Email Lindsay Morris   Send New Private Message       Edit/Delete Post 
Each lamphouse having a specific working distance is tied in with the mirrors used in them.
Most mirrors have a code on them something like 12 x 4 1/4 x 36 which is the mirror diam, the distance from the arc Pos tip to the mirror face and finally the working distance from the mirror face in the centre to the aperture and usually in inches. Have seen some in mm figures.
If the mirror you have is a short working distance and your lamphouse is large/long you will probably not be able to focus the light source correctly. Any old mirror does not suit any carefully.

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