Pin wide body cap on LUMIX micro-4/3. The Pinwide cap is conical, recessing the aperture inside the lens mount close to the sensor.
P1140362 by
Joe Van Cleave, on Flickr
You can see a dust spot on the sensor, upper right corner. Pinhole is a good way to examine your sensor for dust. I wish mirrorless cameras had a lens removal mode that closes the shutter so you can swap lenses. All it would take is a software upgrade.