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cheap RCs
It will be interesting to see how these cheap RCs turn out over time. I am building two carbon truss RCs based around cheaper pyrex Star Instruments 12.5"f6.7 optics. Star Instruments are one of the suppliers for the RCOS instruments, as many here will be aware. My dealings with the optician there impressed upon me that one of the most important aspects of the RC figuring process is the mirror material. They cannot guarantee high accuracy with pyrex because of its relatively uncontrolled thermal behaviour in the optics prodn lab - whereas with the zero expansion material they can reliaby produce very high accuacy mirrors.
I have also learnt that large to very large secondary obstructions and oversize baffling are a fact of life with the RC design in practise. Bringing the f ratio down below f8 or 9 increases field curvature and adds to the secondary obstruction in general. I am looking at around %55 secondary baffle obstruction with my f6.6 optics. The high magnfication factor of the secondary adds another degree of difficulty with the RC. I still expect the Corrected Dall Kirkham designs will prove to be better large flat field performers at the the budget end of the cassegrain astrograph market.
cheers
guy
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