Panasonic Lumix DMC-G2 Operating Instructions Manual page 143

[SHOOT W/O LENS]
•
When using a Leica lens mount adaptor (DMW-MA2M, DMW-MA3R; optional), set it to [ON].
It is possible to setup so the shutter will not operate when there is
no lens on the unit.
[OFF]:
You cannot press the shutter button when a lens is not
attached to the camera body or is not attached
correctly.
[ON]:
Shutter will operate regardless of the lens on the unit.
Advanced (Recording pictures)
VQT2S30
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