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.
Click Here for Quick Balance Reference
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
diagrams below show a telescope on an equatorial wedge, but the procedure is the
same for alt-azimuth mounted telescopes.
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
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.