This paper presents an all-airborne approach for the geometric self-calibration of medium format digital cameras used in direct georeferencing. The motivation for this research was the problems of variation of distortion within the photographic field and high parameter correlations that can result from laboratory self-calibration. Determination of the lens distortion coefficients requires convergent imaging geometry and this is the primary reason why laboratory calibration is normally preferred. We propose an airborne approach that combines the advantages of strong network geometry with the benefit of external data input. Results from a series of simulations demonstrate the capabilities of this approach in terms of interior orientation parameter precision and parameter de-correlation. Experimental results show promising results, especially in terms of the radial lens distortion coefficients.