Five Perf to Viewcard

[P3D <LeRoyDDD@xxxxxxx>]

John Bercovitz said:

"...cameras of the 5-perf format use a normal lens while the stereo 
cameras of the previous century used a little longer lens ... I think Holmes
stereoscopes have lenses of about 7" focal 
length. ... the ratio of focal length to image width is 7 divided by 
3 or 2.3. ... 5-perf ... has an image width 
of 21.4 or so and a focal length of about 35 for a ratio of focal 
length to image width of 35/21.4 or 1.6.  So you can see that in 
the 5-perf format, [with a viewer of more or less Ortho lenses!] you are
sitting much closer to the image ..."

     If I understand John B. correctly, he says (and it's true) if you
enlarge the 35mm film image taken with 35mm length lenses to 3 inch width for
mounting on the "Holmes" format stereocard, you get "stretch" in the Holmes
format viewer. Of course, the regular Realist format *viewers* have a ratio
ranging from 1.8 to 2.3... back to stretch city! :=)
     The solution might be to enlarge the 5 perf negative to 4 inches
(7/4=1.75) and crop out a 3 inch portion for the viewcard images. Nimslo 1/2
frame images also need the 4 inch enlargement to "fit" the focal length of
the typical Holmes viewer, since the camera lens focal length is 30mm.

     But wait! The Nimslo lens separation is 55mm... and the antique views
were often taken on 5x7 inch plates with lens separations of 3 inches or
more!

     Ortho, Ortho, wherefore art thou, Ortho? An elusive condition indeed!

LeRoy Barco
LeRoyDDD@xxxxxxx


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