Re: Still one major hole in telescope offerings

On Sep 24, 7:07 pm, jsav...@xxxxxxxxxxxxxxxxxxxxxxxxxx (John Savard)
wrote:

Actually, though, if one uses plastic lenses - an achromatic lens can be

made from acrylic and polycarbonate - they differ enough from regular
glass that one could use acrylic with standard flint and crown to make a

three-element apochromatic lens that doesn't involve any expensive
materials. But the difference between acrylic and glass is much smaller
than that between fluorite and glass, and so if one is building an f/16
apochromat, the argument could run, what's the point?

John Savardhttp://www.quadibloc.com/index.html

Plastic lenses are not practical because of their very poor physical
characteristics such as anisotropy, poor homogeneity and horible
thermal properties.
.

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