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Re: Taylor-Merchant stereoscope lenses


  • From: P3D John Bercovitz <bercov@xxxxxxxxxx>
  • Subject: Re: Taylor-Merchant stereoscope lenses
  • Date: Tue, 6 Aug 1996 18:37:32 -0700

OK, I looked it up.  The lowest dispersion common optical plastic
has a substantially lower Abbe number than the commonly-used BK7
optical glass although their refractive indices are similar, which
surprised me.  I thought plastic had a lower refractive index.
Well, maybe non-optical plastics do.  Of course you can't get a
really high refractive index plastic that I know of.  So it would 
be tough to make an achromat.  For low dispersion you want a high 
Abbe number so glass wins easily.  On the other hand, I didn't
check window glass and maybe I should.  Who knows how cheap a lens
manufacturer might go?  8-)
 
I just noticed you meant an achromatic glass doublet vs plastic.  No
comparison there.  I don't know how good an all-plastic achromat would
be.  That could be a tough critter to build and get decent results.
Might work.  Could be very cheap in quantity.
 
John B


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