Hello everyone,
I'm considering seriously to start building my own dob.
So after reading a lot of stuff and doing some searching on the web, there are a couple of things i need to ask.
1. Why is it so difficult to find an 18" or 20" aperture primary these days?
And, after finding a couple of interesting cases on e-bay, why do they have to be sooooo expensive?
2. The first question was just to satisfy my curiosity. The second is more practical. Having difficulties in finding a mirror of 18" or 20" aperture, and even if i could find such a mirror i possibly could not afford it, i decided to be realistic. So, i stumbled upon the following 16" inch primary.
http://www.jimsmobile.com/buy_mirrors.htm
Now, does anyone have any experience with these mirrors?
The fact that it's gonna be an obsession-like dob, with trusses, does it mean that the
16" BK7 glass of the primary is gonna be ever-changing during the night and never give me a steady and clear image, making the search for a pyrex-like mirror a one-way road?
Hope i was clear. Being Greek, my English are not perfect.
Thanks in advance!
Alex