The Cooke Triplet: Answering Another of My Own Silly Apochromat Questions

It is my suspicion, therefore, that a refracting telescope based on H.
D. Taylor's design _would_ provide views of the heavens that were
absolutely stunning

There is nothing earth shattering about Taylor's design. It uses one abnormal
dispersion flint in triplet configuration to achieve a modest reduction of
secondary spectrum, not 10x less.

Using NORMAL glasses in any kind of configuration, doublet, triplet, quadruplet
etc. will yield the same color correction as any normal achromat, no matter how
you bend the glass. To get any reduction of secondary spectrum requires at
least one abnormal glass that lies off the Abbe line, and this includes short
flints, and ED/fluorite glasses.

If you have doubts about what I say, then join the ATM Optics software group
and pose it as a challenge to the members:
http://groups.yahoo.com/group/ATM_Optics_Software/

Or you can do some design yourself and will quickly learn what is real and what
is imaginary in optic land.

Roland Christen