A 3D-camera device (1) comprising a Time-Of-Flight sensor (5) and a light guide (4) with a light transparent cover (3). A light source (6) is arranged to emit light (7) into the transparent cover (3), whereby at least a portion (10) of the emitted light (7) is reflected out through a second portion (3.1) of the transparent cover (3) by dirt (100) present on the outer surface (3.20) of the transparent cover (3). The Time-Of-Flight sensor (5) is arranged to receive light (10) reflected by dirt (100) on the outer surface (3.20) of the transparent cover (3) and to output a signal (L) relative the amount of received reflected light (10). A control unit (20) configured to determine the presence of dirt (100) on the outer surface (3.20) of the transparent cover (3) from the magnitude of the signal (L) from the Time-Of-Flight sensor (5).