by Archer Sully
I finally did it! After months of procrastinating, I finally got my 12.5" f/4 back together. When I moved from San Jose to Boulder, the wood in my scope had changed dimension so much that it would no longer stay still. The rebuild has taken me a ridiculously long time, but its all coming together now.
Originally, this scope was a cardboard tube dob. It was somewhat unwieldy, but it sorta worked. It has been reworked into something like an "ultralight" dobsonian, along the lines of http://zebu.uoregon.edu/~mbartels/ul-dobs/ul-dobs.html, but not nearly so nice!
The design is not exactly standard. The UTA is a single ring, with the focuser hanging off a platform, and the spider attached to aluminum angle glued to the ring. The trunnions are 25" surplus from AstroSystems. Mirror cell is very open, its just an aluminum "T" with brass "teeter-totters" that the mirror is glued to. The cell is worth mentioning to anyone building a scope. By using a "T" with collimation bolts at the ends of the "T", the motion is reduced form 3 axes in a standard cell to 2, which is easier to collimate. Also, by having the collimation at the ends, there's more control over the amount the mirror actually moves. This cell is simple to build and I recommend it. A good web page on this type of cell is at
http://www.starastronomy.org/TelescopeMaking/MirrorCell/index.html
The scope isn't fully baffled yet, and there's no finder on it, but I was able to point the scope at M13, which was easily resolved to the core. The lack of baffling prevented me from trying for IC4613 ;-).