The focus drive has two drive speeds. The point at which the change from fast
to slow takes place when moving the focus position to a new value is determined
by the Task Common (TSKCOM) variable FOCS2F, while the stopping window for the
focus is defined by the variable FOCSTP. These parameters may
need to be adjusted at times (see section 
)
, especially if any of the encoders is faulty (e.g. losing
bits), because this is liable to cause oscillation of the focus mechanism, in
particular if the limits are too finely set. Adjustment is exclusively done
by La Palma support staff; the mechanism has proved to be reliable.