Reflector vs Refractor Star Colour

[Earl]

Is there much difference with star colour between an APO and a Reflector?

[Catanonia]

I hardly noticed any other than the ratio between the light gathering of the faster ratio of the newts. I am assuming a proper acro doublet or triplet against a mirror newt.

[ollypenrice]

Depends on how apo the apo is! If it's a really good one and corrected well down towards the UV to the point where the UV/IR filter cuts in then there should be no chromatism. However, that is unlikely...

On the other hand most reflectors need glass in the system somewhere and that will need to be apochromatic as well. Coma correctors, field flattenners etc. all introduce the potential for chromatism. The Ritchey Chretien doesn't have a perfectly flat field but it can sometimes be flat enough to run as a pure reflecting system and I bet Alnitak is less of a hassle in that than in anything with glass in the optical path. (The first RCs used curved photographic plates, I think.)

Olly