Semiautomatic zoom lens calibration based on the camera's rotation

A zoom lens calibration consists of hundreds of monofocal calibrations, each of which takes considerable time and effort with conventional methods.We present a practical calibration method that consists of two separate procedures-zoom calibration and focus calibration. The zoom calibration regards each zoom setting as a monofocal camera, and takes advantage of both the pattern-based and the rotation-based approaches. A rotation sensor is utilized to overcome the ill-posedness caused by the many parameter dimensions. The zoom calibration is followed by the focus calibration process, which is fully automatic and available even at a defocused setting where the pattern detection is not possible. The focus calibration drastically reduces the number of required manual calibrations, from N2 to N times. The experimental results are compared with the lens data sheets provided by the lens manufacturer. The overall calibration procedure is very quick compared to the conventional methods, owing to the proposed zoom and focus calibrations, and shows small enough parameter errors in the effective zoom-focus range.