Qu - Why don't really high-end refractors use carbon fibre instead of aluminium tubes to minimise thermal change induced re-focusing?
Reading up about imaging with APOs - I finally go it that finding and maintain critical focus is a big part of the challenge - and probably why mega expensive, thermal correction, micro calibrated computerised, motorised focuser exist. Phew what a mouthful.
I've re-focused my C9.25 carbon fibre - twice in a year. The Carbon Fibre simply doesn't seem to expand or contract at all - so focus always seems spot one - even when you look really closely. I am sure computer based focusing software would do it a bit better that my eye - but there isn't wild variation.
Why don't high end apos come more commonly in carbon fibre - with its 1/20 the thermal expansion of aluminium? Is it their critical focus zone is so small compared to a SCT that a sub-atomic focuser is always going to be needed
?