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Zerodur or not?

Started by n.i.x, 11/24/2003 08:47PM
Posted 11/24/2003 08:47PM Opening Post
Hi all, in the search for a good Newtonian telescope I'm buying next summer I stumbled accross Orion Optics Uk and will most likely be buying from them. One option to the optical sets or OTA's is a zerodur mirror instead of pyrex. What's the benefit from zerodur? Wouldn't I be better off with the other option; 1/16 surface accuracy , 1/8 PV wavefront? I can't afford both options unless maybe for a 10" aperture but I really want a 12-14".
Thanks
Nico
Posted 11/24/2003 09:00PM #1
Get the higher surface accuracy on a pyrex mirror. Zerodur is a low thermal expansion material, but if you are out of thermal equilibrium you still won't get good images due to air currents. If you are worried about thermal issues, install a fan or fans to cool the primary and/or blow air across the front of the mirror (browse through this group and the telescope making group for tips on using fans).

Jarad