Calibration of focus-adjustable cameras for triangulation sensors by model-based camera parameter estimation

Abstract

Abstract The working range of triangulation-based measuring systems is often limited by the depth of field of the applied optical system. Approaches such as increasing the depth of field range by reducing the aperture are limited in their effectiveness by a lower light yield and thus require a longer exposure time. Focus adjustable optics enable the depth of field to be modified and thus effect the location and shape of the working range. However, the validity of the model-based camera calibration is limited to the corresponding focus setting, especially with optics that exhibit the effect of focus breathing, i. e. whose focal length change with the focus setting. This paper presents an approach to model the calibration parameters over the entire focus range of a lens using function fitting of the camera parameters and the influence of different configurations on this process is examined.