Re: Thoriated Lenses

[Dick King <king@reasoning.com>]

 >Date: Wed, 04 Mar 1998 08:14:42 -0700
 >From: Ronald Morgan <rgmorgan@lanl.gov>
 >To: radsafe@romulus.ehs.uiuc.edu
 >Subject: Thoriated Lenses
 >Message-ID: <3.0.5.32.19980304081442.007ce870@esh-mail.lanl.gov>
 >
 >Hi Folks,
 >I've noticed that most of the better camera lenses I've seen lately are
 >loaded with thorium.  Can anyone tell me why?  It occurs to me that the
 >thorium would increase the density and (surely?) the refractive index, but
 >I don't know enough about optics to know why that would be an advantage.
 >The only thing else that I could think of is that the thorium might boost
 >the temperatures in the casting process...again, why might that be an
 >advantage?
 >Thanks,
 >       **************************************
 >       Ron Morgan <rgmorgan@lanl.gov>
 >       Operational Health Physics (ESH-1)
 >       Los Alamos National Laboratory
 >       MS E-503, Los Alamos New Mexico, 87545 (USA)
 >       Phone (505) 665-7843
 >       Fax   (505) 667-1009
 >       Voice pager 104-1787
 >
 >	 mailto:rgmorgan@lanl.gov
 >
 >       **************************************
 >

To make a good color corrected lens you need two materials with significantly
different refractive indices, and also a high refractive index lets you grind
thinner lenses, yielding less of certain abberations and certainly giving you a
smaller package.

-dk