Quote:
Originally posted by RAJAH235
Will be interesting to see the 'new' DOB when it is released, & the actual optics they pick. Surely they would have to use 'PYREX' for that size!   L.
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Thats exactly what I would have thought.
BK7 (Borosilicate Crown) is an optical glass that was originally designed for making refractive light transmitting elements, not front surface reflective optics. In terms of Newtonian mirrors it is way better than plate glass but certainly not quite as good as pyrex or the more exotic materials in terms of its thermal expansion co-efficient. In smaller mirrors up to 12" it does a very good job and GSO have produced some outstanding BK7 mirrors considering they are mass produced. When you get to a 16" mirror the thermal properties of the glass become a lot more critical than they do in smaller mirrors, this also applies to grinding the mirror as well as observing with it. On the basis that GSO would be ordering a large number of these 16" mirror blanks I would have thought the minimal additional cost of going to pyrex instead of BK7 with mirrors of this size would be well worth it.
I am not sure whether or not the 16" truss scope will ever happen, truss scopes is an area GSO have never gone before, but I would like to think that it can happen. I do know that an Aussie, very experienced in designing and building truss scopes is currently providing them with a lot of design input for such a scope.
CS-John B