P3D Re: In search of "ultimate quality viewing"...

[fj834@xxxxxxxxxxxxxxxxxxxxx (Dr. George A. Themelis)]

Stuart Johnson asks: 

>Also, you mentioned the stereoscopes with achromatic
>lenses?  Are these lenses by themselves obtainable?  Where can I
>purchase one of these scopes?

Keystone offered a line of achromatic stereoscopes used for eye testing. 
The name of the line is "Visual Survey...".  When I got my first one I was
totally impressed by the quality of viewing. I knew right away that
something was different about these lenses.  Later, after discussions
in photo-3d, it was shown that these lenses are "achromatic", made from
two elements instead of the usual one.  Some people might not be able
to tell the difference but for my trained :-) eye there is a big
difference.  With the achromatic lenses there is no chromatic aberration,
infinity is sharper and viewing is more relaxed.  I could see details
in my Visual Survey that had not seen before.

Alan Lewis managed to find a small supply of those achromatic lenses
and created a line of portable stereoscopes. His web page (sorry, don't
have the address here) illustrates and comments on achromatic lenses.
I don't know if he has any more for sale or any lenses left... but
I bet he will find something to replace them, being an ingenious
experimentalist and a sucker for quality too...

After I discovered the achromatic lenses I sold all my stereoscopes
(including the much desired "Red Wing") and only kept the Keystone
Visual Survey and Alan Lewis' scope.  Since then I have found, bought
and sold 3-4 Keystone Visual Surveys here in sell-3d.  My mission is
to get those wonderful instruments out of flea markets, dump basements
etc. and put them in the hands of those who appreciate quality viewing,
like yourself Stuart.

-- George Themelis

PS.  A little writeup on achromatic stereoscopes, a picture of a 
Keystone VS and pictures from Alan's site were in "Stereogram" 2.6
in the special section on stereo prints.


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