Camera Calibration with a Viewfinder

To answer the industrial need for simple camera calibration procedure, we propose a new method that requires a simple calibration object composed simply of a box and two crosses. The box is opened in the front where a large cross, made of wires, is attached while another is drawn (or attached) at the bottom. Both crosses are perfectly aligned similarly to a viewfinder. The viewfinder is first oriented with respect to camera such that the optical axis of the camera passes by the center of both crosses, allowing the display of a single (superimposed) cross and an immediate reading of the coordinates of the optical axis. Then, using the similar triangles theorem, the focal distance can be easily estimated. In addition, if necessary, the method can determine the orientation of the CCD matrix if it is not perfectly perpendicular to the optical axis by solving a simple linear system. This method should be particularly useful for calibration of cameras in situ, such as microscopes or embedded cameras.