An annular fluid-filled sample chamber is used to provide observation of unbounded motion of objects in the fluid. Rotation of the sample chamber is under automatic control to compensate for azimuthal motion of the object, thereby keeping the object in a fixed field of view of an optical observation system. Further motion control can be provided in the radial and focus directions, which can be used to provide full 3D tracking of objects as they move in the fluid. An important application of this work is to observation and tracking of objects that move up or down in the fluid with respect to gravity.