Protection unit (82,92) for an optical probe ferrule (24,47,48,73) of an optical measuring probe of a coordinate measuring machine, the probe ferrule (24,47,48,73) being adapted and arranged to bi-directionally transmit optical signals from and to the measuring probe, wherein the protection unit (82,92) provides for dust-protection of the optical probe ferrule (24,47,48,73) of the measuring probe in an un-mounted state of the measuring probe and is designed so that and is modularly attachable to the measuring probe of the coordinate measuring machine so that the probe ferrule (24,47,48,73) - in the un-mounted state - is protectable against contamination, and transmission of the optical signals by means of the probe ferrule (24,47,48,73) - in a mounted state - is provideable by the protection element (83,93) being positioned in an open-position so that the path is unblocked and the protection unit (82,93) comprises a displacement mechanism which provides automatic displacement of the protection element (83,93) from the block-position into the open-position in the course of mounting of the optical probe. |