Re: Kern-Paillard SWITAR Lens Question

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Posted by Webb on August 27, 2003 at 18:39:27:

In Reply to: Re: Kern-Paillard SWITAR Lens Question posted by Frank Wylie on August 27, 2003 at 14:08:26:

Hi Frank,

Thanks for the info. I tried your experiment. I removed the turret from the Auto-Master and mounter the Switar and a B&H 1" Lumax to the turret (see picture)to check the focal lengths side-by-side. They're darn close. But the best I can tell is that the Switar does have a slightly longer focal length.

I but an arrow in the picture to point out where the Switar lens protrudes through the back of the turret.

Thanks again!
Webb

: Yup, its a C mount, but it probably has a modified backfocus for reflex shooting on a Rex 4 or 5.

: You can do an informal experiment; take a "normal" C mount lens (one you are sure works properly on your b&h) and lay it next to the Switar. Focus both lenses at infinity and an identical aperture. Line the flange shoulder of each lens up (NOT the rear or front elements) and shine a light into the lenses.

: Now, take a bit of paper and find the backfocus of the "normal" C mount; where the light source filament is sharpest. It it the same on the Switar? Is the Switar slightly to the rear of the "normal" C mount?

: Reflex bolex lenses have a deeper backfocus to make it focus through the reflex prism; your B&H doesn't have that provision, so a shallower (standard) C mount backfocus is used.

: Good luck

: Frank

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Comments:
: Hi Frank, : Thanks for the info. I tried your experiment. I removed the turret from the Auto-Master and mounter the Switar and a B&H 1" Lumax to the turret (see picture)to check the focal lengths side-by-side. They're darn close. But the best I can tell is that the Switar does have a slightly longer focal length. : I but an arrow in the picture to point out where the Switar lens protrudes through the back of the turret. : Thanks again! : Webb : : : Yup, its a C mount, but it probably has a modified backfocus for reflex shooting on a Rex 4 or 5. : : You can do an informal experiment; take a "normal" C mount lens (one you are sure works properly on your b&h) and lay it next to the Switar. Focus both lenses at infinity and an identical aperture. Line the flange shoulder of each lens up (NOT the rear or front elements) and shine a light into the lenses. : : Now, take a bit of paper and find the backfocus of the "normal" C mount; where the light source filament is sharpest. It it the same on the Switar? Is the Switar slightly to the rear of the "normal" C mount? : : Reflex bolex lenses have a deeper backfocus to make it focus through the reflex prism; your B&H doesn't have that provision, so a shallower (standard) C mount backfocus is used. : : Good luck : : Frank

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