Re: Star D & lenses

[SCHUB@xxxxxxxxxxxxxxxxxx]

John Bercovitz writes:

> Et tu, Martin?  I'm really shocked.  This list has gone from
> being the kinder and gentler list to the ad hominem argument list.

Sorry for the abrasive tone of my post.  I hope you'll be charitable and
put it down to enthusiasm.  I didn't mean to come off as ad hominem--the worst
thing I said about you (actually the only thing) was that you were wrong.
    I see that I'm wrong about the parallel rays.  I had always assumed that
the way magnifiers work is that your eyes focus on a virtual image, but I
guess I can see how it might be a strain to do that for a long time if the
virtual image is only, say, 6" from your eye.  So, thanks to you and Jim
Crowell, I can now understand why the lenses would be focused to give parallel
rays.
     So why _does_ it strain the eyes so much to look through pre-Holmes-Bates
stereoscopes that use two complete lenses (rather than half lenses)?  The
feeling I get when I do this is that my eyes have to work hard on convergence,
not focus or other things.  And why do plastic stereo lorgnettes and molded
splastic stereoscope lenses mimic the shape of the split-lens originals?
It doesn't seem likely that it's just so that you can see the whole image,
because you can see the whole image in the pre-Holmes-Bates models.  Also, the
constraints on lens diameter are not nearly as stringent here as in 35mm.
     Again, sorry I was so abrasive.  Time to take some meds, I guess (insert
the "Medication Waltz" from "One Flew Over the Cukoo's Nest"...)

						Martin


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