Balancing an Equatorial Mount

The next step in the setup of your equatorial mount is to balance it in the two dimensions corresponding to the two axes of movement.

Why Balance?

Balancing your mount is an important step (often overlooked by beginners). A balanced scope will move more smoothly and will tend to stay where it is put until you move it, while an unbalanced scope will have jerky motions, be unstable, and tend to drift. Worse, an unbalanced scope puts more load on the gearing in the slow-motion controls, and can cause the small motors in a motorized scope to overload and burn out.

Getting Ready

Complete the assembly of your mount, including the counterweights and attaching the telescope.

Load up the telescope with all the accessories you are likely to be using in tonight’s observing session: the finder, dew shield, diagonal, and an average-sized eyepiece. Include the camera if you will be doing photography. The idea is to put the amount of weight on the mount that you will be using for the evening.

Balance in Declination

First, we’ll balance the scope on the declination axis, which is the motion around the counterweight shaft.

Loosen the clutch that stops the mount from moving on the Right Ascension axis and turn this axis so that the scope is sticking out to one side of the mount, roughly level with the counterweight at the other side. This gives room to allow the optical tube to rotate on the Declinaion axis. Tighten the RA clutch so the scope stays in this spot.

Holding the scope in one hand to prevent it from crashing into the mount, use the other hand to loosen the clutch allowing motion on the Declination axis.

The scope will probably flop to one side or the other, as it is probably not balanced.

Adjust the balance by moving the scope forward and backward – either by loosening the mounting rings and sliding the tube back and forth in the rings, by sliding the dovetail back and forth in the mounting plate, or whatever other means your mount has of moving the balance in this direction.

In some rare cases – usually involving a light telescope connected to a heavy camera – you may not be able to slide the OTA (Optical Tube Assembly) or dovetail far enough to reach balance. In such cases you may need to buy or build some kind of counterweight that fits onto the OTA or dovetail (usually the dovetail, near the front) to help achieve balance.

In the above photos no such “declination counterweight” is needed. In the photo to the right, as an example, a home-made counterweight (a hunk of brass) is bolted on to the underside of a lightweight OTA, near the front, to offset the weight of a heavy camera on the back.

Continue adjusting until the scope balances in Declination without being supported. Then tighten the Declination clutch again.

Balance in Right Ascension

Next, we will balance the mount around the Right Ascension axis.

Temporarily slide the counterweight all the way to the top of its shaft and tighten it there. Then, holding the telescope with one hand, loosen the clutch that stops the mount from moving on the Right Ascension axis enough so that it can move freely.

Carefully let the scope flop to the side, which will happen because the scope is putting weight on its end of the RA axis. Don’t let it free-fall! Help it down gently with your hands.

Loosen the clamp holding the counterweight and slide it back along the counterweight shaft, then check the balance again.

Continue adjusting the counterweight until the scope will balance evenly on this axis.

Small mounts will come with a small counterweight suitable for a small telescope (or with the supplied telescope if purchased as a kit). If you change to a larger telescope, or add a camera or heavy accessories, you might need another or a larger counterweight.

Return the scope to its normal upright position, and tighten the Right Ascension clutch so it stays there.

Results

Congratulations, you have now balanced your telescope in both dimensions of motion. When you later move the scope to find or track objects, it will be well balanced and smooth and, if you have electric drive motors, you will have minimized the work they have to do.