The hatches of the 3.6m allow four different openings:
|Open hatches||Available sky area (altitude)||Available sky area (Zenithal distance)|
|4||90 - 58 degrees||0 - 32 degrees|
|4+3||90 - 42 degrees||0 - 48 degrees|
|4+3+2||86 - 24 degrees||4 - 66 degrees|
|4+3+2+1||68 - 7 degrees||22 - 83 degrees|
Typically hatches # 4,3,2 are opened. Care has to be taken for observation at Zenith, as Hatch # 2 covers 4 degrees at Zenith when it is opened. In case of need the Hatch # 2 can be closed from the control room, but reopening it requires the telescope operators to drive up to the telescope, leading to an overhead of about 10 minutes.
For observations below 24 degrees of altitude the hatch # 1 is vignetting and should be opened implying, also in this case, an overhead of about 10 minutes.