Re: Achromatic StereoScope

[P3D Dr. George A. Themelis <fj834@xxxxxxxxxxxxxxxxxxxxx> To: photo-3d@xxxxxxxxxxxxxxx]

>> This discussion made me curious enough to open and take apart the >>lenses in my Keystone 46B Visual Survey Telebinocular. >> Unlike every other stereoscope that I have seen, this one has no >> chromatic aberration and delivers pin-sharp images.... >
>I remember the discussion on this list. I have seen a couple of metal >Keystone viewers (the library pedestal and the hand held telebinocular >that stores in the fake book). Is the model you mention one of these? 

No, I have seen plenty of those and they all have single element lenses. 

>In John Waldsmith's "Stereo Views" book he lists a Keystone telebinocular, >metal,viewer that came in a booklike box and adds that it has >excellent optics. Is he referring to achromats? 

No. The optics in these ones might be marginally better than older scopes but are not achromats.

>Or is yours a vision testing instrument rather than the typical consumer >models? Do you know about what year your viewer was offered? 

Yes, I believe it is. Many of those were used in schools for testing vision. All the ones that I got came with eye testing views and scoring cards. I believe they were all used in schools. The series of testing cards is very interesting since it tests all aspects of vision from convergence to stereopsis to accommodation. The last one I saw was bought in a school sale and it had more plastic parts and was lighter but had the same quality optics. One of the report forms that came with the scope says "Keystone Visual Survey Tests" and it is copyrighted 1951. I like the idea of testing someone's vision with a set of 13 cards via a stereoscope... 

>If it was ground from two separate pieces then I would expect to see a >molded edge rather than a perfectly flat sawcut edge. >Thanks for the offer to send them to me, but I'd rather you don't. I >shudder to think that they could get lost or damaged. 

This one looks like a flat sawcut edge. I'll send it to you. It's OK. If you loose it you will just have to give me one of your pairs... ;) 

>I would love to be able to offer an achromat scope as a continuous >product. When I run out of lenses I'll go into a depression. 

Why is it so difficult to find a similar lens from Edmund or other optics place? The price will be high, but you only need one lens ;) 

Regards -- George Themelis


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