Specify how the focus distance changes with elevation.

Mandatory Arguments:

Double f10...f90

The optimal focus distance, in millimeters, specified at intervals of 10 degrees in elevation, from 10 to 90 degrees.

Example:

The following command specifies the measured or fitted optimal focus positions at elevation angles of, 10,20,30,40,50,60,70,80 and 90 degrees.

 focus_curve -29.87, -24.73, -20.33, -16.68, -13.76, -11.59, -10.15, -9.46, -9.51

Context:

The receiver at the focus of the telescope can be moved a short distance along the optic axis, to accomodate changes in the optimal focus positon. The focus position along this line varies as a function of elevation, in a way that has to be measured empirically. The focus_curve command allows one to specify how the focus distance changes with elevation, for use by the focus command. The focus_curve command requires that optimal focus distances be given for each of 8 specified elevations. The focus command linearly interpolates between these values, to determine the optimal focus distance for the elevation that the telescope is currently pointing at.

Note that until the focus_curve command has been invoked to define the focus curve, all points on the active focus curve are set to zero focus distance. So this command should ideally be invoked from a setup script before observations commence.

For the highest frequency receivers, it may be necessary to install different focus curves for different temperature ranges. This can be done using the tfocus_curve command. When this is done, the focus curve specified by the focus_curve command is still used if the current temperature isn't covered by any of the temperature-specific focus curves.