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View Full Version here: : Why don't really high-end refractors use carbon fibre instead of aluminium tubes?


g__day
06-02-2008, 03:33 PM
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 ;)?

MortonH
06-02-2008, 04:16 PM
Some do. Check out

http://www.tetontelescope.com/index.php?cPath=53_12_28

If you look at the prices, I think your question is answered!!!

Morton

Phil
06-02-2008, 04:23 PM
Depend where you are imaging the focus will change no mater what the tube is made of. I find at bigging of imaging i may be closer to the east
and when i get closer and closer to the zenith the focus will change a little.
Phil

Kal
06-02-2008, 06:53 PM
A quote from Roland Christen from Astromart forums (http://www.astromart.com/forums/viewpost.asp?forum_post_id=501926&poll_id=&news_id=&page=) (you need to be a member to view)