Jump to: navigation, search


To make the Direct Drive with high resolution encoders to work for unguided exposures we need a way to correct for position errors in real time.

There is no ideal telescope and several errors can occur during slewing and tracking.

The main errors can be:

  • Polar alignment error in Azimuth and Altitude
  • Collimation error (optical axis not paralell with mecanical axis)
  • Mount error (axes not perpendicular)
  • Tube flexure
  • And several gearing errors, mount flexure etc.


The software can compensate for all these errors as long as they are reproducible (same error every time the telescope point at a position).

To compensate for these errors they first have to be measured. This is achieved by a pointing file.

A pointing file is a list of pointing observations specifying where the star really was and where the telescope readouts said the star was. These measurements are saved in a file.

The software work with a set of functions that describe the telescope pointing with the listed errors (Polar alignment, Collimation, Mount error). All these functions have certain variables. These variables will be optimized so that the set of functions will optimally describe the telescopes pointing behavior that was measured with the pointing file. This set of variables is calculated from the pointing file data and saved.

The ASA software making these correction are called Autoslew.

Example pointing file content