carbon or aluminium

[Davey-T]

Didn't want to hijack Dans' thread so wondered what are the percieved benefits of carbon fibre are over aluminium for apo refractor tubes ?

Still saving for new, big trip apo and see that Skywatcher claim that aluminum is better for the Esprit range, why do they

claim this to be so ?

Dave

[DirkSteele]

Actually I have heard from one premium Apo maker that carbon fibre tubes are a fools errand as the lens cell is still made from aluminum and the different coefficients of expansion will result in undesired consequences. Far better the entire scope expands and contracts in unison. Of all the very high end Apo makers (Astrophysics, APM, Televue, Takahashi et al) I can only think of one who uses Carbon fibre, and that is Officina Stellare. That might also indicate something.

Carbon Fibre scopes do look nice though. My Nexstar 11 GPS OTA is carbon fibre but aluminium at both ends.

[ollypenrice]

Good points above. Carbon has low expansion but high thermal insulation. The premium apo makers don't use it. I tend to think they know more about it than I do.

Olly

[wouterdhoye]

If I'm not mistaken there are two things:

a) as Olly mentioned carbon is a bad thermal conductor so it would take longe rfor the air in the telescope to cool

the glass of a refractor is also expanding and contracting with temperature. the result is that a zero expansion carbon tube would actually behave worse in regards of keeping focus than a aluminium or steel tube.

on reflector telescopes where glass is used with very low to even irrelevant expansion the benefit of a carbon tube is noticable though. But still at the expense of longer cooldown times, even with open tubes. Though if you set up early enough this is a minor issue as the telescope can adapt long enough then.

but carbon tubes do look mighty cool :-)

kind regards,