For many applications, a fork-mounted telescope will be sufficiently balanced as it comes from the factory. However, precise balance becomes critically important when taking astrophotos or when using heavy accessories such as 2″ eyepieces. Proper balance causes less wear on drive motors and allows the telescope to track more accurately. In our experience, most tracking errors are caused by an improperly balanced telescope. Learning to balance a telescope is easy and can be an essential technique for many applications.
First, we will look at how to balance a telescope, then discuss the ideas behind balance so you can better understand it.
Quick Balance Reference
Balance Vertically First
- 1. Point telescope vertically
- 2. Carefully loosen clutch
- 3. Push telescope lightly in each direction to determine balance
- 4. If telescope is top-heavy (toward finderscope) add weights to the bottom of the scope
- 5. If telescope is bottom-heavy (away from finderscope) add weights to the top of the scope
Balance Horizontally Second
- 1. Point telescope horizontally
- 2. Push telescope lightly up and down to determine balance
- 3. If telescope is front-heavy, slide weight toward the back of the scope
- 4. If telescope is rear-heavy, slide weight toward the front of the scope
For more specific details, read the section below, then print out the above Quick Reference to have with you in the field.
Balancing a Fork-Mounted Telescope
It is very important to balance the scope in a vertical position first! The most common balancing error is to reverse these steps. See the section at the bottom of the page for details why this procedure is critical.
1) Begin by aiming the telescope straight up. If the telescope is top-heavy (due to the finderscope, etc.), you will need to add weights to the bottom, usually by use of a counterweight slide bar as seen below. Some telescopes come with a slide bar, but for most scopes this will be an additional accessory.
Above: If the scope is top-heavy (toward the finderscope, or right in this picture), add weights to the opposite side until balance is achieved. If the telescope is bottom-heavy (toward the counterweight bar) remove weights until balance is achieved. When you are close to balance you may need to give the scope a gentle push in each direction to tell whether more adjustment is necessary or not.
2) After the telescope is balanced vertically, point the scope horizontally. You can now move the sliding weights to balance front to back.
Above: If the telescope is front-heavy slide the counterweights toward the back (eyepiece/camera-end) until the scope is balanced. If the scope is back-heavy slide the counterweights toward the front (away from the eyepiece/camera) until balance is achieved.
Why do you have to balance a fork-mounted telescope vertically first? The reason lies in the position of the center of gravity. If you do not balance a fork-mounted scope vertically first, the center of mass of the tube is offset, meaning the position of the counterweights front-to-back on the scope will be incorrect. Even if the telescope seems balanced in one position, when pointed to another area of the sky it may not be balanced.
If the telescope is not balanced vertically first, the center of gravity (CG) will be displaced. In this example, the telescope is too heavy toward the counterweight and the center of gravity is low. This will cause the counterweight, when balanced horizontally, to be placed too far forward.
If the telescope is balanced vertically first, the center of gravity is in the correct position. The counterweight, when balanced horizontally, ends up in the right place and the telescope is properly dynamically balanced.