Actually, there is no inherent advantage of CaF2 over say FPL53 in astronomical instruments. Fluorite's main advantage (transparency deep into UV spectrum) is completely negated by a practical mating element which is from 'main sequence' and as such will be completely opaque in UV. It
is very useful in modern silicon chip manufacture where UV is used to "print" semiconductor elements smaller than a wavelength of green light (e.g. 30 nanometer technology, these days pushing 22nm). But for
telescopes its advantages are moot.
Designing a doublet is far from rocket science; it is actually very easy. All you need is a mating glass of same partial dispersion (P f,e) and as wide as possible difference in Vd. If we look at today's available glass we can see that CaF2 line offers a few nearly perfect mating choices. But so does FPL53. In fact there are BETTER practical choices for FPL53 glass; ZKN7 is a well known (and used, notably by AstroPhysics) match and it offers marginally HIGHER polychromatic Strehl than say CaF2 + K5 combination which is often suggested. See
http://www.telescope-optics.net/semi...o_examples.htm
and compare entries 15 and 16 (which are best doublet designs).
Calcium Fluorite (being a perfect crystalline structure)
does scatter less than any fluorocrown glass (which is amorphous), but difference will be invisible in real life. First, there's that mating element, and second, quality of polish and coating will dominate the final at-the-eyepiece result. Although still a tricky material, it is far easier to work with FPL glass (and get that nearly perfect polish) than it is with CaF2. And multicoating of fluorite was not even done until recently (early Vixen and Takahashi doublets had its CaF2 elements uncoated).