Optical camera calibration for cas navigation

A navigation system for tracking an object in a sterile field during surgery, comprising:

• at least one marker adapted to be connected to the object in a known relation, the object being used in the sterile field during surgery;
• an optical camera detecting a light signal from the at least one marker, the optical camera generating tracking data associated with a position of the at least one marker from the light signal;
• a shield on the optical camera, the shield being positioned between the optical camera and the at least one marker during surgery to allow at least a portion of the optical camera to be within the sterile field;
• calibration data associated with an effect of the shield on the light signal passing therethrough to be detected by the optical camera;
• and
• a position and orientation calculator for calculating at least one of a position and an orientation of the object as a function of the tracking data, of the calibration data, and of the known relation between the object and the at least one marker.