Zoom-dependent calibration for consumer grade-cameras

A significant practical constraint currently applying to the adoption of consumer-grade digital cameras for photogrammetric measurement is the requirement to record images at fixed zoom and focus settings. This is a consequence of the variation of camera calibration parameters, especially principal distance and lens distortion, with changing zoom and focus. This paper describes a zoomdependent calibration model, in which the image coordinate correction equations for departures from collinearity are expressed as a function of the nominal focal length written to the EXIF header of the images. Such a calibration approach frees the user from the constraint of recording images with both fixed focus and zoom. The newly developed zoom-dependent calibration approach is reviewed and the results of its application to the calibration of a number of off-the-shelf cameras are presented. The benefits of the approach for medium-accuracy close-range photogrammetry applications across fields as diverse as traffic accident reconstruction and heritage recording are then highlighted.