Resurrection Scope

A month ago, there was an announcement on our local astronomy group’s web page about a telescope that had been found in the garbage. Was anyone interested in seeing if it could be rescued? I responded right away because I had in mind a project that required an optical tube.

I made a call and got directions to come pick up the relic. The scope was rescued from the trash by a friendly fellow. He got a bike that he wanted and he knew someone in the SAAA and found out how to post a notice that he had this “partial telescope”.

When I went to collect the scope, I learned from the neighbor that the scope had been in a lady's garage since 1985. She had recently died and her extended family had thrown out several things that were considered useless by them. The home was off Ingram Rd just inside 410 in San Antonio.

The scope was originally put together by her son, I learned. He was 16 years old when he went to China on a youth missionary trip in 1985. He contracted an infectious disease and died there. His family was unable to even bring his body back to the US because of fears of the infection. I was told they eventually got him buried in Hawaii. If anyone ends up knowing anything about this unfortunate telescope builder, drop me a line and I will update the entry here.

The scope was about a dirty as could be expected from sitting unprotected in a garage for 25 years. It was the optical tube from a reflector telescope. There was a 1.5 inch sighting scope screwed into the tube next to a broken down focuser. The secondary hung by a wire from the focuser and bounced back and forth like a scared kitten. The mirror was labeled on the back as American Optical and had a focal length of about 67 inches.

I disassembled the finder scope and cleaned the lenses. It was usable, though the mount was not of the modern type that fits into a base. The tube had a strange collection of nuts all strung out on an unreinforced two inch long 3/16 inch bolt at about the balance point. Maybe it had once been attached to a tripod by that bolt.

I removed the mirror cell and then the mirror. I submerged the mirror in a tub of water with a little detergent. After soaking, I gently removed the accumulated crud on the mirror with a series of surgical cotton balls. I used each one for a very short cleaning stroke. After cleaning the mirror in this way, I rinsed it with water out of my Culligan filter and then touched the corner of a paper towel to each water drop that did not run off the mirror surface when it was hung vertically. There was one small flaw in the mirror coating about an eighth of an inch in diameter and my work did not seem to have introduced any scratches in the coating.

I reassembled the mirror cell with double sided sticky tape and checked out the optics. Even though the focuser was very difficult to use, and the secondary holder bobbed around, I was able to see that it would focus and give me a decent image.

So I set about doing what I had intended from the beginning. I started building a large diameter altitude bearing dobsonian mount.

I designed the altitude bearing to be two feet in diameter and wrapped the tube in a box a foot long. I made the altitude bearing half moons to be removable with knobs made from bolts and washers. I built the base from two round circles 20 inches in diameter. All these were made from ½ inch hardwood plywood, with the altitude half circles made in double thickness, an inch thick.

I made the bearing surface of each axis from fiber reinforced plastic with sliders made from pieces I cut out from a kitchen cutting board.

I designed a saw blade spring secondary spider to replace the original bouncy secondary holder. The new one is rock solid. I also bought an inexpensive ($40) 1-1/4 inch focuser from Orion.

The project cost about $45 in wood, $45 in hardware, and $40 for the focuser. It ended up being a reasonable deal for a pretty nice 8 inch scope. It also helped me to explore several technologies I needed to understand for my project intended to replace the stock base of a Meade 16 inch Lightbridge.

The photograph shows all the pieces. I had taken them apart to varnish all the surfaces. It was a good photo opportunity. All edges were routed to make them approximate a half round. The bearing surface of the half circles was also routed but not as deeply.