Lenses for the red button...

[P3D Dr. George A. Themelis <DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>]

These older viewers have very sharp lenses.  The one I was working with
appeared to have a problem, distortion, did not look good.  I took apart
the lenses and, sure enough, one was placed backwards.  I put it properly
and now it is as sharp as it can be.  The viewer had a bunch of cracks
and would not sell for much.  So, I decided to keep it for myself.  My
second (yes, just second... unlike Allan C. who is rumored to have two
dozens) red button viewer!  Looks junk, works great!  Usual Dr. T 
philosophy.

This is the 4th time that I see this problem.  Achromatic lenses are not
symmetric front to back!  They need to be installed in a specific way.  
If one or both lenses are installed backwards, bad distortion will 
result, detectable by the sharp eye of Dr. T.

Just the other day I replaced the lenses in a white button Realist viewer
(these have single-element lenses) with Revere achromatic lenses.  These
are identical to the Realist in diameter and focal length.  They are
good!  I used to believe that the Realist lenses were better... now I
am changing my mind (but still prefer these older viewers and some newer
ones, with black button are good too).

So... make sure that your lenses are installed properly and consider
putting Revere lenses if you are not satisfied with the quality of the
image.  In addition to single-element white-button Realist viewers, there
are many Realist red buttons that have fog between the elements or other
distracting problems... Consider a pair of Revere lenses for these viewers.

Where to get the Revere lenses?  From Dr. T, of course!  He can install
them for you too!

George Themelis


------------------------------