Mechanical aperture for controlling illumination level

In an illumination system for a film telecine scanner of the type adapted to provide a line of illumination on the image frames of a film which is supported for movement in a film gate of the scanner and comprising a light source which is adapted to provide a generally circular light beam in an optical path in said system, and light integrating means located in said optical path for receiving said light beam and for producing a line of diffuse illumination on said film, aperture setting apparatus for selectively adjusting the amount of light entering said integrating cylinder in response to the commanded light intensity signal within the time span of scanning a single image frame of the film. The aperture setting apparatus comprises a housing containing a continuous, single piece, elongated band having first and second centrally disposed light obstructing or solid band sections formed in parallel planes with respect to one another and first and second light transmitting or cut-out band sections separating the first and second light obstructing band sections and forming end loops of the elongated band, the first and second shaped leading edges formed as edges of the first and second light obstructing band sections defining one side of the first and second respective light transmitting band sections which face one another and interrupt the light beam in near the same plane as the first and second light obstructing band sections are moved in parallel with respect to one another and the opening. In order to support and move the elongated band, a tension and return idler assembly supported by the housing engages and provide rotational and tensioning support for the end loop of the first light transmitting section. A motor drive assembly supported by the housing engages and provide rotational driving force to the end loop of the second light transmitting section. Idlers supported by the housing means guide the first light obstructing band section into closely spaced parallel relationship with the second light obstructing band section. A position sensor provides a position feedback signal to the illumination control system for providing servo regulation of the positioning of the aperture defining leading edges of the band.