Re: Ultraviolet "Barlow" lens?


"Louis Boyd" <boyd@xxxxxxxxxxxxxxxxxxxx> wrote in message
news:fcu5co$k07$1@xxxxxxxxxxxxxxxxxxxxxxxxx

Thank you for the help Dave. You've pretty well confirmed my suspicion
that there isn't a simple or inexpensive solution to this problem.

Louis, if you used a simple CaF2 singlet, you would get less chromatic
aberration than you would with a fused silica singlet. It so happens that 2
inch diameter, -500 mm focal length CaF2 singlets are currently in stock for
$355.00 at ISP optics:

http://www.ispoptics.com/store/index.php?main_page=index&cPath=4_33_83

If you aren't familiar with CaF2, it is a reasonable material. It is very
weak and soft when compared with fused silica, but it is quite suitable in a
normal laboratory environment when used with care. Not sure about your
observatory conditions. You do need to take care when mounting it when
large temperature ranges are expected; it has a very high coefficient of
thermal expansion.


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