re: closeup lens focus

[T3D john bercovitz <bercov@xxxxxxxxxxx>]

Dick Koolish writes:
 
> If the primary lens is set to infinity, it would be expecting parallel
> rays.  For the closeup lens to produce parallel rays, the subject would
> have to be at the focus of the closeup lens.  So wouldn't you measure
> the subject distance from the closeup lens?  Or is this analysis too
> simple?
 
Well, that's the way it seems to you, and that's the way it seems to Michael 
Gordon, and that's even the way I always thought it was, and furthermore 
that's the way my camera thinks it is (I just tried it with a +3 and a +2), 
but when I read the aforementioned lens combination formula, it doesn't seem 
that way at all.  So obviously I'm misinterpreting the formula.  I'll get 
back to the group after I figure out how I'm misreading the situation.  I'll 
also do some more careful optical measurements after I make a proper mount 
for my camera on my optical bench.
 
Thanks,
John B
 


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End of TECH3D Digest 63
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