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

[siggyblue@xxxxxxxxx]

--- In tech-3d@xxxx, cfholzner@xxxx wrote:
> --- 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
Thanks Chuck.  I all ready know about increasing the focal length 
to match the print enlargement.  the problem is the viewer F.L. is 
around 230mm. If I were to preportionally increase my views they 
would be much larger than is possible to view.
What do you mean by ortho?  
When you say a longer focal length "increases the depth".  Do 
you mean the viewers perception of depth?  Or are you referring 
to the actual distance from lens to print?
Thanks,
David   


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