A shutter assembly , comprising: a first shutter blade having a first toothed arm extending therefrom, the first shutter blade having a first light transmitting aperture therein; a second shutter blade positioned adjacent and parallel to the first shutter blade, the second shutter blade having a second toothed arm extending therefrom, the second shutter blade having a second light transmitting aperture therein, the first and second shutter blades supported to allow parallel linear motion; and a motor having a gear disposed between, and meshed with, the first and second toothed arms (30; 34) such that rotation of the gear causes the first and second shutter blades to move linearly in opposite directions between an open position in which the first and second light transmitting apertures (32; 36) are in an overlapping relationship with respect to one another, and a closed position in which the first and second light transmitting apertures are in a non-overlapping relationship with respect to one another; wherein the shutter assembly further comprises a first reference aperture in the first shutter blade positioned between the first light transmitting aperture and the second light transmitting aperture to align with the second light transmitting aperture in the second blade prior to alignment of the first and second light transmitting apertures in the open position, the first reference aperture being positioned along a center line connecting the first light transmitting aperture and the second light transmitting aperture, such that overlap of the first reference aperture with the second light transmitting aperture provides an indication of the movement of the first and second shutter blades between the closed position and the open position. a first shutter blade having a first toothed arm extending therefrom, the first shutter blade having a first light transmitting aperture therein; a second shutter blade positioned adjacent and parallel to the first shutter blade, the second shutter blade having a second toothed arm extending therefrom, the second shutter blade having a second light transmitting aperture therein, the first and second shutter blades supported to allow parallel linear motion; and a motor having a gear disposed between, and meshed with, the first and second toothed arms (30; 34) such that rotation of the gear causes the first and second shutter blades to move linearly in opposite directions between an open position in which the first and second light transmitting apertures (32; 36) are in an overlapping relationship with respect to one another, and a closed position in which the first and second light transmitting apertures are in a non-overlapping relationship with respect to one another; wherein the shutter assembly further comprises a first reference aperture in the first shutter blade positioned between the first light transmitting aperture and the second light transmitting aperture to align with the second light transmitting aperture in the second blade prior to alignment of the first and second light transmitting apertures in the open position, the first reference aperture being positioned along a center line connecting the first light transmitting aperture and the second light transmitting aperture, such that overlap of the first reference aperture with the second light transmitting aperture provides an indication of the movement of the first and second shutter blades between the closed position and the open position. <EOS>