Film-Tech Forum ARCHIVE: Light efficiency with 62.5 mm v/s 70.6mm diam. lenses

This is topic Light efficiency with 62.5 mm v/s 70.6mm diam. lenses in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Jerry Axelsson (Member # 3175) on 07-08-2012, 05:11 AM:

Is there any difference in light output/efficiency in a modern 35mm projection lens (3-5 years old). If you compare the same lens model in a 62.5 mm diameter version and a 70.6 mm diameter version?

Posted by Richard Fowler (Member # 893) on 07-08-2012, 07:16 AM:

I have found next to none differences in most lenses since the glass is manufacturered in modular form to fit as many situations in their product line. I see the same situation in some camera lenses we service....many common metal "plumbing" parts to make an end product.

Posted by Steve Guttag (Member # 268) on 07-08-2012, 08:23 AM:

It is only going to make a difference as you approach 140mm EFs. Schneider and ISCO's lenses below 100mm (and for ISCO above 40mm or so) are identical with respect to 62.5 and 70.6mm. The outer most lens barrel (hollow) is all that is different. On lenses like the Kiptar...unscrew the outer most silver sleeve and you will have a 62.5mm barrel on the inside.

Posted by Jerry Axelsson (Member # 3175) on 07-08-2012, 09:04 AM:

Thanks for the info guys.