How do I manually change the focus of the telescope?

The focusing is automatic, it is made by a system based on different temperatures measured on the tube of the telescope (autofocus) and acting on the position of the secondary mirror M2.

Manual changes are made in the prompter-T120.

The mirror can be positioned in an absolute manner

@m2p <absolute move>

or relative manner

@m2p [+|-]<relative move>

Attention, you must limit yourself to 1 parameter only because this command also allows you to modify the X-Y displacement and the X-Y tilts with parameters 2 to 5.

The nominal positions are

NECAM:
$THOME/config/t120/applic/ecam/server.cfg
te.m2zpdef = 25.408

CORALIE:
$THOME/config/t120/applic/coralie/server.cfg
te.m2zpdef = 32.250

The current focus can be extracted from the night log files with:

grep -a "best focus at" $TDATA/services/MAINTENANCE/log/2020-01-02/t120.*

LW 27/04/2020