Re: Star D and lenses

[bercov@xxxxxxxxxx (John Bercovitz)]

>     OK, I now believe the argument that you don't need interocular 
> adjustment in a viewer if you have large-diameter lenses whose 
> center-to-center distance is the same as the infinity-point separation 
> of the slide.  But what if you encounter a slide that's not mounted 
> very well, and has and infinity-point separation that doesn't match the 
> viewer-lens separation?  You have to diverge or converge your eyes to 
> fuse it, right?
 
That's correct.  To counteract this, infinity points have about 63.5 mm
of separation and lenses have about 65 mm of separation.  So you're always
converging in a correctly-mounted slide.  However, since vergence is a 
relatively weak depth clue, you don't notice it.  Disparity is the strong
clue and it overrides.  This system errs on the side of convergence because
minimal amounts of divergence are uncomfortable to the unaccustomed viewer.
 
John B


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