How can I use GoTo Approach to minimize backlash with my Fork arm mount?

To minimize backlash with your mount, use your hand control and select Menu – Scope Setup – GoTo Approach. This will let you choose the direction the scope will use when approaching an object during the final part of slewing–the ideal way to minimize backlash. 

The directions can be either positive or negative and are defined as seen from the back of the scope. For altitude, positive moves the front of the tube up, negative down. For azimuth, positive moves the front of the scope to the right, negative to the left.

Always set the direction of approach in the opposite direction from the load pulling on the scope. This minimizes effects of backlash in the gear train. The load in altitude is usually because of gravity acting on the scope’s imbalance from accessories (eyepieces and the like). The load in azimuth is due to tracking and is opposite (in reaction) to the tracking direction, so the approach direction will be the same direction as tracking.

Whether to set positive or negative in altitude or azimuth depends on your scope, the type of mount, its orientation, Southern or Northern Hemisphere location and the load from attached accessories.

In a typical situation with Schmidt-Cassegrain (SCT) telescopes, the tube will be back heavy, because you have attached accessories to its back. The load acts to pull the front of the tube up–positive–so the opposite direction–negative–should be chosen for GoTo Approach.  For azimuth, the tracking of the scope determines the loading. The telescope tracks to the west–positive (from behind the scope)–so the GoTo Approach should be set to close in from the same direction, moving west–positive.

Many users use the default setting, which is altitude negative, azimuth positive. For the SCT with a star diagonal, GoTo slews will be seen as moving to the up and right with these settings.

In the Southern Hemisphere (from behind the scope), west is to the left, reversing the GoTo Approach settings for azimuth.

Note: when aligning the mount, use the same approach directions to center your alignment stars as you are using for GoTo Approach for the best GoTo performance.


Updated 12/21/13