Counterbalancing a Telescope
In order to apply weights to balance a telescope, you must equate the moments (weight times distance from the axis of rotation). For example, to compensate for an especially heavy eyepiece or other accessory on a typical Dobsonian, the counterweight may need to be several times the extra weight you are trying to balance. The fulcrum (altitude axis) is seldom halfway between either end of the tube. With a heavy mirror, the fulcrum is much closer to the mirror end, so you have to add at least twice as much weight at the mirror end to counterbalance the weight added at the eyepiece end.
To figure out how much it will take to counterbalance the accessory, take into account the moments, not just the individual weights.Published in the October 2000 issue of the NightTimes