Catadioptric omnidirectional sensors (catadioptric cameras) capture instantaneous images with panoramic 360 field of view. Entire surroundings are projected via a circularly symmetrical mirror onto the image. Nothing disappears from view even when objects move and the robot rotates. Therefore, catadioptric cameras are very effective in dynamic visual guidance applications such as tracking of objects, obstacle avoidance, site modelling, mapping, simultaneous location and mapping (SLAM), visual guidance, and navigation. Computation of image velocities (optic flow) is central to dynamic computer vision applications in robotics. This paper exploits the specific properties of catadioptric projection via conical mirrors to derive a simple direct solution for optic flow, named Omni Flow to emphasise its omnidirectional scope. Unlike earlier optic flow methods, Omni Flow is non-iterative and therefore better suited to real-time robotics applications.