Leica S2 Instructions Manual page 84

6. Shutter speed pre-selection in BULB mode
In BULB exposure mode (B), the extended menu can be called
up by pressing the click wheel. The difference exposure times
can be directly preselected by turning the click wheel. The
click wheel has to be pressed again to confirm the selection.
The set exposure time then appears in the OLED display.
4 / Firmware Update 1.0.0.24
7. Extension of setting options for AF/AE lock button
The functioning of the AF/AE lock button (1.17) can now be
changed.
First of all, it differentiates between autofocus (AF) and
manual focus (MF).
MF mode
In MF mode, the AF/AE lock button can be assigned the
following functions:
AFs on - Single autofocus
AFs on / AE-L - Single autofocus and exposure value lock
AFc on - Continuous autofocus
AFc on / AE-L - Continuous autofocus and exposure
value lock
AE-L - Exposure value lock