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Ian,
Well I know the corrector plates in the Meade 14 are 11mm thick for example. The smaller SCT's will have thinner glass, but this is offset by the smaller diameter. I have seen the calculation done for the Meade 14 corrector plate and to cause a deflection of 11 micron at the end of the hyperstar (~200mm out) requires a force of 25 lbs (or 12 kg!). A more typical camera would cause closer to 1-2 micron deflection - pretty minimal.
To actually break the corrector requires a lot more force, and the person who did the calculation above used 1000psi as the Ultimate tensile strength of glass calculated 140 lbs at the end of the hyperstar. However, the Ultimate tensile strength for glass is >4000 psi, so even factoring in local stress raising factors ( around the secondary hole) it wouldn't suprise me if the corrector couldn't support the weight of a person. Anyone like to test this!
According to Starizona the instances of broken corrector plates have been from people shipping the scopes with the hypestar still attached. But the have also noted broken corrector plates caused by shipping of standard SCT's! As an aside, back in 1997 when I travelled to the US to see Comet Hale-Bopp while I was waiting at the baggage couresel I watched a baggage handle throw a foam wrapped cylindrical package across a room where it bounced end-on-end until it final came to rest against the other baggage. At the time I remember thinking that it looked all the world like a Celestron/Epoch 8" f1.5 schmidt camera wrapped in black foam...anyway the moral is you can never be too careful when shipping a scope!!
Anyway, back to the hyperstar this morning I was able to test under very hazy conditions with lots of high cloud and getting final collimation is going to take a bit of effort. 10-15 minutes of collimation adjustment was initially required to get acceptible images and there is more adjustment to do, but the potential is impressive! Attached is a small crop around the horsehead from a 30 second exposure using a QHY9 unbinned. Stars down to mag 17.5 are visible as expected.
Terry
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