How to Properly Calibrate the Reticle of the Polar Scope to Increase Star Tracking Precision
About the author
Stefano Ciurleo is an IT architect at GME (Italian Power Exchange), where he has worked since 2002.
Prior to 2002 he worked in industrial automation and machine vision.
He is an amateur nature photographer and astronomer with a passion for travelling.
MSM: Stefano Ciurleo, an Italian photographer and a guitar enthusiast, happens to be one of our users and we can't thank him enough for taking the time writing such a lovely tutorial for all night sky fans. You can check out more about him on Flickr and find this tutorial in Italian on his shared Notebook.
In order to obtain maximum precision in tracking the apparent motion of the stars, the axis of rotation of the reticle must be aligned with the axis of rotation of the polar scope.
To check if the reticle is centered, you have to collimate an object such as an antenna, a roof, or a power line pylon while daylight time and rotate the polar scope on its axis. The center of the grid must always remain on the selected point.
If the reticle results to be off-center, you will need to proceed with the calibration. The process may not be easy for everyone, so before making any changes, I recommend making some shooting tests in order to check if the accuracy is fine enough for your own purpose. However, the more centered the reticle, the longer the tracking time achievable.
The reticle frame is connected to the polar scope with three Allen screws. To correct the position of the reticle, the three screws must be adjusted.
With an Allen wrench, do very small adjustments tightening a screw after releasing opposite screws to move the reticle according to compensate the deviation from the center. Do very small movements and check the status rotating the polar scope. Repeat the operation until the reticle is calibrated to the center.