Re: Viewer interocular (was RBT mounts... - alignment)

[P3D <PgWhacker@xxxxxxx>]

Paul Talbot writes:

>
>I have noticed that some mounting problems can seem to magically disappear
>as the interocular is changed.  Before describing my theory as to why this
>is so, I'd like to hear thoughts on the question "What is the proper way
>to set the interocular of a stereo slide viewer?"
>


Ferwerda's book has a nice chapter explaining the optics of stereo 
viewers.   With diagrams.

The proper way to set the interocular is:  with the optical center wider 
than the stereo pair's inifinity point separation.

  It's worthwhile understanding that a stereoscope's lenses have two 
kinds of separations.  Physical and optical.  The _physical_ separation 
is the distance between the physical centers of the lens chips.  The 
_optical_ separation is the distance between the _optical_ centers of the 
lenses.

    In many old Holmes stereoscopes, and in modern $4 Added Dimension 
lorgnettes, the optical center of each lens lies outside, 'lateral to,' 
the physical center.    In these stereoscopes the physical lens are not 
made from the optical centers of a round lens, instead they are 
(optically) chips taken from the edge of a much larger lens.  Because 
they are thicker on their lateral edges than on their medial edges, they 
are often called 'wedge' lenses, though I suppose the term would offend a 
purist.  They aren't really wedged, they are simply cut (conceptually) 
from the edge of a larger lens.

   At any rate, this is an extremely clever and subtle setup:  it lets 
anyone, provided their inter-eye distance fits within the broad limits of 
the physical separation of the two lenses,  view stereographs with much 
wider than humanly possible image separations -- up to the _optical_ 
separation of the two lenses.  Without having to diverge their lines of 
sight.  

  The "optical center wider than the stereo pair's inifinity point 
separation" also applies to Red Button, Green Button, etc viewers, whose 
optical and physical centers are identical.




Greg Kane
Denver

PgWhacker@xxxxxxx





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