T3D V-M format viewer lenses

[john bercovitz <bercov@xxxxxxxxxxx>]

FWIW:
People often ask me what the focal length of the lenses in V-M viewers 
is and I always say, "Around 50 mm." because that's about how far the 
lens is from the reel.  Well, I just got a bunch of viewer lenses from
John Dukes, manufacturer of the Dukes 12X viewer as sold by Dalia.  He
has plenty on hand because he converts stock viewers in an aesthetic way
and the first step is to cut off the lens housings.  I just measured the
lenses on my optical bench and here is what I found.

V-M old glass lens from bakelite viewer or new plastic lenses from 
plastic viewer, focal length is 47 to 47.5 mm.  Clear aperture on
the plastic viewers is 14 mm.  I don't know what it was on the old
bakelite viewer but I think smaller.  IPD of the new viewer was 64.8.

Meopta plastic lenses, 40 mm focal length and 13 mm clear aperture.
IPD is 65.4.

All lenses are equiconvex presumably so they can't be assembled into the 
viewers backwards.

John B


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