Lecture Notes in Computer Science 1 Calibration Update Technique for a Zoom Lens

Abstract. A technique for a zoom lens camera is presented that enable to update continuously camera intrinsic parameters while zooming. This is based on the fact that the spatial angle subtended by the optical center and the same two 3-D points in the standard camera coordinate system remains invariant for subsequent image frames on which the two 3-D points are located. The new focal length value is obtained as the solution of the quadratic equation we derive from the angular invariance. We give an error estimate to show how the uncertainty in the localization of corresponding points in the image frames may affect the accuracy of the updated value of the focal length. We report the results of two experiments when sequences of magnified images were taken by fixed and by rotating camera. 1