1. An older thread on iceinspace.com.au covered essentially the same topic as posed for this thread -
Calcium fluoride vs Fluorite vs Fluoro crown
In the iceinspace.com thread, posts by Bratislav provided technical background for a comparison of FPL-53 and CaF2 in refractors, including, in part, the same telescope-optics.net page cited by Alan French in his post starting the present thread.
Bratislav began his outline with a simple statement:
"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."
He then provided the tech details supporting that statement in the same and successive posts.
2. Given Roland's choice of FCD100 in the new Stowaway 92, replacing the FPL-53 used in other recent Astro-Physics triplets, vs. Yuri's choice of fluorite in place of FPL-53 in the updated TEC 140, I am taking the liberty of trying to extend this discussion to FCD100 -- 'Comparing FPL-53, FCD100, and CaF2'
Is there yet data for FCD100 triplets with 'ideal' mating glass(es) like the data on the Vladimir Sacek telescope-optics.net page cited by Alan French in his original post? What exactly is the significance of the Astro-Physics claim that the new Stowaway 92 provides 'unprecedented color correction'? In 'Color correction' specifications provided on A-P's Web sites describing the Stowaway 92 and the GTX 130, the color spectrum spanned by the 0.005% focus-variation criterion is actually somewhat narrower for the Stowaway than for the GTX.