In this tutorial we have studied three design criteria of catadioptric sensors: (1) the shape of the mirrors, (2) the resolution of the cameras, and (3) the focus settings of the cameras. In particular, we have derived the complete class of mirrors that can be used with a single camera, found an expression for the resolution of a catadioptric sensor in terms of the resolution of the conventional camera used to construct it, and presented detailed analysis of the defocus blur caused by the use of a curved mirror.