Godfrey Finn's telescope
12-inch
f/5.3 Newtonian
After reading many books, and seeking advice from experienced astronomers in the NNHS, my son Nicholas and I considered various options, and finally decided to build a Newtonian reflector on a Dobsonian mount. The optics were purchased, but the rest of the instrument was constructed by ourselves. The octagonal tube is made of 9-mm ply with 20-gauge formed aluminium angle fixed inside, and the box mount is also made of 9-mm ply. The mirror cell is made of 19-mm MDF, stiffened for stability, and is mounted at three points round the edge - one of them a universal joint, and the other two on strong spring-tensioned mounts. Two collimating rods enable adjustments from the top of the tube. The diagonal mirror is on a three-arm curving mount. These and other metal parts were made by my son-in-law Stuart. A strong triangular base was constructed, and the turntable is fitted with a two-way spirit level, rotating in azimuth on three fixed castors. Turned trunnions are fitted inside sections of 7-inch gas-pipe to facilitate altitude adjustment. Setting circles are also fitted, and we use the StarTrak program on a hand-held Psion 3. The tube splits into halves, and the box hinges to fold flat, so that the entire instrument can be dismantled to fit into a car.