Quote:
Originally Posted by gregbradley
When you say there is no gain using the carbon fibre tube over the aluminium - are you saying the focal point isn't stable with temp shifts?
That is the usual reason for carbon fibre tubes - so the focus stays stable even with falling temperatures.
Aluminium typically should mean focus will be shifting as temps fall and will require refocusing on a regular basis. Not true with this model?
Greg.
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I fully agree Greg. The fact that both mirrors are held by, in effect 2 big lumps of aluminium focus shift will happen. The shift shouldn't be that great with Al having a thermal coefficent of 23.
I do have similar concerns for carbon fibre rods etc used in telescope making due to the fact that the carbon fibre has a very low thermal co-ef but the epoxy resin it is held solid with is another matter entirely and without knowing the make up of this resin it is dificult to know what expansion and focus shift can be attributed to the resins used. The woven scrim of carbon fibre used is designed to allow for some expansion without breaking the carbon fibre strands which have a very low shear strength.
I think the difference between the carbon fibre and Aluminium model of this scope will be very negligable in fact probably very hard to measure or confirm that any difference at all exists.
A scope like yours which has the secondary supported entirely by the carbon strutts may be a different kettle of fish. Time and experience will tell in both cases.
The GSO optics look pretty good on an initial quick image and star test so for the price I am very happy.