Attempt to change the focus position of the receiver.

Arguments:

Double position

The desired focus position (mm).

Example 1:

The following example tells the control system to attempt to change the focus position to 45mm.

  set_focus 45.0

Context:

The optimal focus of the telescope changes with elevation. The set_focus command allows one to compensate for this by changing the position of the receiver feed along the bore-sight of the telescope.

The focusing mechanism of the 40m telescope moves at 1.6mm/s, and has a range of 180mm.

The time taken for the focus mechanism to home in on the specified position, is unpredictable. Completion of the operation can be awaited using an until statement with the acquired() function, as follows:

  until $acquired(focus)

To determine whether the operation terminated successfully or failed to acquire the target position, use the focus_acquired() function.

If the focus operation fails, this could mean that the configured focusing tolerance is too high. The focus tolerance is initially configured by the focus_drive_pars command, but may subsequently be changed using the focus_tolerance command.