Installing achromats

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

Be careful when installing achromats!
 
I was working on a red-button Realist viewer today.  When I was all 
done and had put everyting back, I took a look and was shocked at the 
distortion of the image.  My first thought was that someone replaced 
the original Realist lenses. 
 
On second thought, I decided to take out the lenses and check if they 
are installed properly.  (Taking apart the viewer after putting it 
together is a pain...)  Sure enough, the lenses were reversed.
 
Achromats are not symmetric.  It is important that they are installed 
properly.  Usually the two elements show a different thickness along 
the side.  When you take a lens apart, just mark down which side faces 
the eye and put it back the same way.
 
This particular lens had a cracked body and the lenses had defects in 
between the elements.  My theory is that someone had a viewer with 
good lenses and cracked body and another with bad lenses and good body 
and decided to switch the lenses around to keep the good lenses and 
body and sell the bad lenses and body.  In the process of doing so, he 
messed up and installed the lenses backwards.  I only hope that he has 
the lenses in his good viewer reversed too...
 
This the second time that I get a viewer like that.  The first time I 
had no clue and returned the viewer with a note that the lenses are 
not as good as the normal Realist lenses.  Now I know better...
 
George


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