14 inch dob
This is a 14.25 inch f/5 scope that I made in 2005. The mirror is from a BVC blank that I ground and polished with the help of the Mirror Lab of the St Petetersburg Astronomy Club. The mirror is supported by a nine point flotation cell. The eleven inch long optical tube is cardboard reinforced by a layer of fiberglass.
The three aluminum truss tubes have an inside diameter of 1.75 inches and have threaded inserts in both ends. The lower tube ring has three threaded rods inserted to attach the truss tubes on one side and the mirror cell on the other side. The knobs that hold the mirror cell to the lower ring also collimate the primary mirror.
This scope is based on ultralight telescopes made by Albert Highe, BobSmith, and others.
SketchUp view of cell
Mirror Cell
The shroud is made from some collapsible containers that are sold as containers for yard waste, coolers, hampers, etc. To attach the shroud to the scope I use bungee cords at the bottom (mirror box) and self-adhesive Velcro pads and strips at the upper end of the optical tube. The shroud made from two 22 inch tall containers came out short, so I had to add an eleven inch strip of nylon. To make the hole for the focuser, I used the focuser tube to mark a circle in the shroud. I then ran a bead of glue on the mark, and after it dried I cut out the nylon up to the glue. The glue should keep the nylon from fraying. The completed shroud weights about two pounds, and cost less than $50.00 to make.
Updated in 2012
Small reversible gear motors handle two of the three collimation adjustments.
The limit switches stop the cell from crashing into the tube ring or backing out to far. When wired this way the motor can still be run in the other direction when stopped by one of the switches.
The miter gear on the collimation bolt is threaded. This moves the spring load mirror cell to move in and out when rotated by the motor.
The elevation encoder and the stalk for the Sky Commander module mount to the inserts used for one of the wheelbarrow handles. The stock encoder mounting arm was not long enough so I used a piece of scrap plastic instead.
