Rotary wheels are one of  basic blocks of  systems for testing imaging EO systems.  They are needed to enable motorized exchange  of active target  at collimator focal plane.  There are usually 8 holes in the wheel for targets (other numbers are also possible). Wheels are covered with a black high emissivity coating (emissivity at least 0.97).

Design of rotary wheels looks apparently simple but practical manufacturing is no so easy. Ultra precision positioning (high repeatability) of the wheel is  the main design challenge.  Positioning uncertainty of the rotary wheel at level below 0.05 mm is expected in case of systems for testing imagers used for automatic target recognition systems.