first project, secondary questions...

Well, I spent my anniversary at my the local telescope making workshop (it was okay, the husband had a gig...and I was so excited to start grinding-first time!). I wanted to go ahead and pre-order a Telekit kor the f/5 12.5" mirror I'm making (not too skilled carpentry-wise, thought I'd be better off with a kit), and they're asking me about secondary sizes. I see this was an issue here for a while. Randy at Astrosystems recommended a 2.6" secondary- do you agree? Any recommended sources for high quality secondaries?
Mary

I had a 12.5"/f5.2 that I used a 2.5" diagonal and it worked very well. It was a case of already having the 2.5". Astrosystems had to make me a secondary holder for it as 2.5 is no longer a standard size. So, you may as well go with the 2.6" so the holder won't be an odd ball size.

Walt

2.6 or 2.14 are the obvious choices. 2.6 would be "better for deep sky with a more fully illuminated field," and 2.14 "may give slightly better contrast for planetary viewing." There is a theory that central obstruction should be held to about 20% for best contrast, and 2.6 at 21% it pretty damn close. The 2.14 still looks good on the SEC program, and a 17% central obstruction. 2.6 is probably the more conservative all around use choice. But, I don't think that you could go too far wrong with either, and people do change there secondaries on occasion so it's not cast in stone.