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Sorry for the late post to this discussion , but I thought that I had better correct a few misconceptions about optics etc.
It doesn't matter what the substrate is of your mirror when you are using it! Truly! An extra couple of minutes of cool down makes not that much difference. The substrate does matter when you are MAKING a mirror as you have to wait for the polished mirror to cool down between testing. Hence: CERVIT, ZERODUR & PYREX (Duran50).
Eardrum73 said:
"Mirrors - Comes with pyrex parabolic mirror which means you will get some out of focus bits on the edges. But thats with all scopes that uses curve mirrors, some roughness at some point."
Who told you this? I am sorry to say that you are wrong. You will not get "out of focus" bits at the edges just because it's pyrex, unless you used pinking shears to cut out the disc. A parabola will be generated from edge to edge in the same form. That's why we do zonal testing on mirrors as the defect will form in a radius from the centre. We correct the 70% zone or the 30% zone, we never correct for radial errors. as they hardly ever occur (unless you are using plate glass and hold the mirror before immediately polishing it, or if the disc has internal strain).
As for the old Coulter scopes, their mirrors were ok at the time, as were their prices, but I remember seeing quite a few that were undercorrected as they assumed that once mounted the mirror would sag to the correct figure, wrong!
The Coulter scopes used a one bar spider. It was about 5mm thick and the collimation of the secondary was done with one bolt which was mounted off axis to the centre of the secondary mirror cell. This system did not make collimation fun.
The Coulter mirror was not mounted terribly well either. Even a six or nine point flotation system would have been better than the way they did it.
So actually the BINTEL or GS Optical tube assemblies are much better with their four vane spiders, good mirror cells and collimation (even if they are three point collimation and not orthogonal).
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