What is backlash and how can I adjust it?
April 3, 2007
Backlash is play in the drive gears. All telescopes have some backlash, as gears cannot be too tight, preventing the motors from turning. Backlash causes the delay in scope movement when using the direction arrows on the hand control. It is especially a problem when moving in the direction opposite the scope’s tracking, when the lag before the scope moves can be on the order of 10 seconds if the backlash is bad.
The goal is to minimize backlash, and the good news is your Celestron scope’s control firmware lets you to do this by rewinding the motors enough to eliminate the gear play when the arrow is pressed and winding it back the other direction when the arrow is released to make the gears re-engage and go back to smooth tracking.
Positive backlash compensation is applied when the mount changes its direction of movement from backwards to forwards. Negative backlash compensation is applied when the mount changes its direction of movement from forwards to backwards. When tracking is enabled, the mount will be moving in one or both axes in either the positive or negative direction, so backlash compensation will always be applied when a direction button is released and the direction moved is opposite to the direction of travel. The amount needed will depend on the slew rate; slower slews will be more sluggish and will need higher values. Visual work will be less demanding and won’t need as high values as guiding for astroimaging.
One general tip: Always use the up-and-right for final alignment to match the direction the scope will use to approach an object during a goto. This helps to reduce the backlash inherent in any system and improves goto and tracking accuracy.
Refer to either your manual or the Knowledgebase article for your scope model for specifics on backlash settings: German GoTo mount or Alt-Az GoTo mount.