[tech-3d] Re: Different F.L.s

[cfholzner@xxxxxxxx]

--- In tech-3d@xxxx, siggyblue@xxxx wrote:
> I have these stereo viewer/books I made.  The lenses I put in 
> them are the inexpensive plastic holmes print viewer glasses 
> sold by reel-3d.  At the time I made them I didn't know that viewer 
> focal lengths should match the camera's.  The only camera I 
> have now is a 35mm. Is there an adjustment I should make if I'm 
> using the Bercovitz formula?  The each view print is 60mm wide.
> David

I don't know about the Bercovitz formula but I think I can put some 
light on the subject.  
The viewer lens FL should match the Camera FL for ortho viewing if 
the print is the same size as the negative, as it would be with 
slides.  When you print from the negative and enlarge the image you 
should enlarge the FL of the viewer the same.  Enlarging from 23 mm 
to 60 mm is an enlargment factor of 2.6 and so you should use 2.6 X 
35 mm  (91.3 mm) viewer lenses.  This is still short of what the 
Holmes lenses are, mine are in the range of 180 mm.  Very few people 
are viewing ortho so it probably doesn't matter.  The longer FL in 
the viewer increases the depth and many prefer it.

Chuck


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