UCLES and UHRF have Hartmann masks to aid focussing. The UCLES Hartmann
consists of a half-circular mask which may be driven in front of
the collimator and rotated into either of two positions.
The UHRF Hartmann mask consist of two barn doors which can be
opened or closed as desired.
Relevant commands: (UCLES) HP UP/DOWN/OTHER
Relevant commands: (UHRF) HP UP/DOWN/OTHER/SHUT/OPEN