I have been observing with a Coulter 10" dobsonian since 1988. It has been a wonderful instrument for general observing and I have enjoyed making many improvements over the years, including the installation of smooth teflon/formica bearings. Despite the use of counterweights, I have had ongoing problems with preventing unwanted motion in altitude, particularly during star parties when everyone seems to want to lean on the telescope while observing. This is particularly a problem with changing eyepieces, especially heavy Naglers, when the telescope is not perfectly balanced. After some difficulties at a windy star party a few years ago at the Boston Museum of Science, I designed a simple and very effective altitude brake and slow motion control which can be assembled very quickly and at minimal cost.

The slow motion control consists of a short wooden arm connected to the center of the altitude bearing with a large plastic knob with 1/4-20 thread, which acts as a clutch. The other end of the arm attaches to a turnbuckle*. The opposite end of the turnbuckle attaches to a bolt attached to the rocker box. When the clutch is loosened the telescope moves freely in altitude. When the plastic knob is tightened, rotating the turnbuckle leads to small movements in altitude which easily centers the telescope at high power. A wooden drawer knob provides a convenient grip to turn the turnbuckle. The unit also acts as a brake which is particularly helpful when changing eyepieces, in windy weather, or at star parties. I highly recommend this simple approach to solving a common problem.

* I recommend a marine quality turnbuckle which can be obtained from the Dwyer Aluminum Mast Company, Inc., North Branford, Connecticut (203-484-0419).