Abstract: A single lens range sensor comprises a camera 27 having a pair of plano-convex lenses 28a and 28b, an optical mask 30, an imaging sensor 32, a digitizer 34 and a computer 36. The optical mask 30 may be implemented with a liquid crystal array having spatially varying opacity which can be switched (e.g., by the computer 36) between masks derived from a differentiable mask function and its derivative. Alternatively, the mask 30 may be composed of two printed masks which are mechanically switched to obtain two images based on the differentiable mask function and its derivative. The imaging sensor 32 may be implemented with a CCD array. The invention avoids the correspondence problems of the two camera and moving camera approaches, and is simple to calibrate.