>I too am interested in a 12" f/8 mirror.
Larry: Thanks for your reply. My goal for this project is super-planetary work, and so figure is going to be very important. BTW, I have a Coulter 13.1" so I'm not really looking for deep-sky. I intend to build it to use the same dob rocker box. As far as mounting goes, I have heard differing opinions re. how thin a mirror can be -- see Mel's message. I have a 9-point mount for my Coulter mirror to try, and/or shag carpet, bubble pack, etc. Say, how about a Sorbothane sheet? Or an 18-point cell. The plate glass is about $25, so I have thought about glueing two together. In re. thermal expansion, I realize that I missed a factor or two in the analysis I tried last night, and that ignoring the differing thickness of the mirror along the radius is not good -- I think that may be a much bigger factor. In any event, it seems clear that at f/8, the problem of the mirror being used at a different temp than it was figured at will be minimal. BTW, I started wondering because it has been almost 90 degF this week, and if I figure it like this, what will happen when I want to use it in the winter, at 5F? I'll be sure to let you know what happens.
Take care, Peter Augello