Making your telescope orthogonal using the Sky Commander!

When using Digital Setting Circles (DSCs) such as the Sky Commander, the mount, saddle, mounting rings, and telescope must be at right angles to each other (orthogonal). The DiscMounts are designed to be orthogonal, but the saddle, mounting rings and telescope must be orthogonally adjusted as well. The following is one method of adjusting the telescope, saddle and mounting rings using the Sky Commander and the star Polaris (see note below for using terrestrial objects in the day time). The North Star is used because it is stationary and at a convent height above the horizon.

1) Enter the Set Up menu by holding down, both the UP and DOWN arrow on the Sky Commander and turn it ON. Using the DOWN Arrow, select “SIDEREAL CLOCK” then select OFF and hit ENTER (U-turn arrow). Turn the Sky Commander OFF.

2) Turn the Sky commander ON, set the date and choose any two stars for alignment to get the Sky Commander in it’s operational mode. There is no need to actually point the scop at the alignment stars. Hit the UP arrow so the asterisk and arrows are displayed.

3) Point the telescope at Polaris and center it using a high power eyepiece. The higher the power the more accurate the adjustment (the minimum should be 100X). Using an eyepiece with crosshairs is also good.

4) In the Sky Commander menu, select REALIGN ON OBJECT and hit ENTER. The display will read ALT = 000.0 and AZ = 360.0

5) Slowly move the telescope to the opposite side of the mount (180 degrees), the telescope will be pointing south. Swing the telescope with the ALT axis so the telescope is again pointing north. Now center Polaris as close as possible by viewing it through the eyepiece. The AZ on the Sky Commander should read 360.0 (we are not concerned with the Alt reading), otherwise the dovetail must be shimmed to compensate for the error. By shimming the rings where they are attached to the dovetail, the rings and telescope will be aligned together. The amount of shim depends on the amount of error and the distance between the rings. The shim should be placed between the ring and dovetail and then the mounting screws tightened. As an example, my NP101 clamshell required one thickness of notebook paper, my TAK Mewlon required four business cards. Note that the collimation of the optics will change the adjustment, so reflectors should be in collimation before making the telescope orthogonal. It is also best to use straight through viewing rather than diagonal (some diagonals are not at perfect 45 degree angles).

6) Each time a shim is used, start the procedure at step 3 and retry until the AZ is as close to 360.0 as possible.

7) When the adjustment is complete, go to the Set Up menu (as in step 1) select “SIDEREAL CLOCK” then select ON, hit ENTER and turn the Sky Commander OFF.



The telescope can be made orthogonal in the daytime by using a distant object, the accuracy depends on the distance the object is, and how well the object can be centered. For most small telescopes one mile is adequate. Use an object such as a bolt mounted on a power pole.