achromatic viewer

[P3D Peter Abrahams <telscope@xxxxxxxxxx>]

I have wondered why my Telebinocular has such thick lenses.  Examining the
picture of the disassembled lenses at
>http://www.arlington.net/homes/dlewis/projects/achrom.htm
shows that the doublet is .88" thick.  Can any reader inform me as to an
optical basis for the use of such thick glass?  A color corrected doublet
is not usually so thick.  This is a short focus lens, but in general the
thickness of the glass apart from the steep curvature of the surface does
not serve an optical purpose.  The picture also shows a third element, to
add prism for divergence, similar to a simple stereo viewer.
The Telebinoculars are wonderful viewers, so I'm not arguing with success.
I'm just wondering if there is some principle of achromatic magnification
illustrated here.

As George says:

>And now I can die happy 

Are your viewers in your will?  I'd hate to think of the violence at the
estate sale if it's a free for all.
_______________________________________
Peter Abrahams   telscope@xxxxxxxxxx
the history of the telescope, the microscope,
    and the prism binocular


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