The numerical aperture of the illumination and projection optics at the DMD optical area must be the same. This cone angle defined by the numerical aperture must not exceed the nominal device mirror tilt angle unless appropriate apertures are added in the illumination and projection pupils to block out flat-state and stray light from the projection lens. The mirror tilt angle defines the DMD's capability to separate the "On" optical path from any other light path, including undesirable flat-state specular reflections from the DMD window, DMD border structures, or other system surfaces near the DMD such as prism or lens surfaces.