1. A method for optical self-diagnosis of a camera system adapted to record a stereo image obtained from at least two partial images, the method comprising: a) recording a first partial image and a second partial image of an object space with the camera system from different perspectives; b) producing a depth image from said first partial image and said second partial image on the basis of parallax between mutually corresponding pixels recording said first and second partial images, and determining disparity values representing said parallax; c) determining a number of valid disparity values of the depth image, wherein a valid disparity value is defined as a disparity value which is determined for two pixels, recording the first and second partial images, which are identified as being mutually corresponding either unequivocally or at least with a defined probability; d) producing a warning signal depending on the number of said valid disparity values.