Film-Tech Forum ARCHIVE: Lens turrets on 35/70 machines

This is topic Lens turrets on 35/70 machines in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Andrew McCrea (Member # 674) on 08-25-2006, 11:49 AM:

Hey everyone,

I've seen 35/70 projectors with lens turrets (Flat/Scope), but I've noticed in literature it says that the turrets are for 35mm lenses only.

Is this because the 70mm lenses are too big and heavy to be rotated in a turret?

If you have a 35/70 machine with a turret, where/how do you put the 70mm lens in? Do you just switch out on of the other lens (scope/flat) or something, or could you just get a three lens turret and use the empty third one?

Posted by Aaron Sisemore (Member # 145) on 08-25-2006, 12:09 PM:

Many of the older 70mm lenses were 4" diameter and therefore wouldn't fit in a turret to begin with.

The newer 70mm lenses are the same physical size as a 35mm lens- I don't see why they wouldn't work, (weight-wise they would weigh less than a full-size anamorphic) unless the turret doesn't have the facility to alter the optical center between the two formats.

-Aaron

Posted by Andrew McCrea (Member # 674) on 08-25-2006, 12:46 PM:

One more question then; bear with me as I don't completely understand the optics behind lenses, but what is the optical centre and what would the alteration be?

Posted by Scott Norwood (Member # 30) on 08-25-2006, 01:12 PM:

The image on a 35mm sound print is off-center with respect to the film because the soundtrack occupies one edge of the film. The projector lens mount is normally located at the center of the image area and the lens normally needs to be re-centered for 35mm silent prints, 35mm mag-only prints, and 70mm prints, where the image center is centered with respect to the film. Usually, the lamp alignment needs to be tweaked as well, and 70mm requries a beam spreader lens.

The only 35/70 machines with turrets that I have seen are the JJs at Brad's screening room and he can run 70mm just fine.

Posted by Brad Miller (Member # 2) on 08-25-2006, 03:59 PM:

Scott, I have since switched the left projector back to a single lens head. Dealing with the gate design on a turret is a major bitch, as the only good way to set the clearance and tension is with film running and the gate isn't spring loaded at that point, it is latching.

Posted by Gordon McLeod (Member # 33) on 08-25-2006, 04:38 PM:

The Victoria 8 had a 4" diameter lens turret
and the wetrex 5000 had a 3 lens turret marked flat scope and 70mm