Film-Tech Forum ARCHIVE: Where Is The Optical Center Line?

This is topic Where Is The Optical Center Line? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Pete Lawrence (Member # 130) on 10-17-2003, 05:16 PM:

What's the standard for the horizontal optical centerline on a projector? Is it the center of the film or the center of the image frame? Is it the same for different manufactures?

Posted by John Anastasio (Member # 607) on 10-17-2003, 06:58 PM:

It's the center of the image, not the film itself.

Posted by Michael Schaffer (Member # 1204) on 10-17-2003, 08:57 PM:

Since you had bad luck with the "pinhole" plate you might either try your luck with the Align-O-Tron ( www.muellersatomics.com ) or see if you can get one of those string kits traditionally used by Strong. Ask your dealer - they come with every console, maybe you can even have one for free.

Posted by John Pytlak (Member # 331) on 10-18-2003, 06:58 AM:

The centerline of the projectable image area is specified in standard SMPTE 195-1998. It is 0.738 inches (18.75mm) from the reference edge (soundtrack side) of the print. It is offset from the actual centerline of the film by 0.050 inches (1.27mm).

Some projectors allow shifting the lens mount for the different horizontal centerline originally used on 35mm CinemaScope (magnetic sound only) prints that had an aspect ratio of 2.55:1.