Re: Ultraviolet "Barlow" lens?

Opto Sigma has a line of UV achromats that you might look at. I don't know
how they would do for you application, but they are CaF2/fused silica
doublets as I recall.




"Louis Boyd" <boyd@xxxxxxxxxxxxxxxxxxxx> wrote in message
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Dave Schaack wrote:
"Louis Boyd" <boyd@xxxxxxxxxxxxxxxxxxxx> wrote in message
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I have a need for an achromatic "barlow" lens to effectively convert a
20" diameter F/4 Newtonian telescope (parabolic mirror) to F/8 and
extend it's focal plane location a few inches. It needs to have
reasonably low chromatic aberration and good transmission from 300 to
600nm. The Edmund 50.8mm x -500mm fl PCV fused silica lens would work
were it not for the focal length shift versus wavelength. . Any ideas or
sources for such a lens? I can afford up to about $1k. The lens also
needs to act as an entrance window so it can't be a delicate material.


If you need 50.8 mm diameter, I doubt that you can do it within your
budget. However, at smaller diameter, I think you could afford a custom
Calcium Fluoride singlet and a catalog lens. You may be able to combine
a CaF2 singlet with a catalog fused silica singlet to form an achromat
that would do the job. If you need it to be robust on both sides, then
perhaps you could use two fused silica singlets of half the power, that
is, make a triplet.

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.


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