Rotating prism optical system

Claim 1

IN MOTION-PICTURE APPARATUS OF THE TYPE IN WHICH FILM TRAVELS CONTINUOUSLY AND AT A UNIFORM RATE THROUGH A FILM PLANE AND PAST A FILM APERTURE CENTERED ON AN OPTICAL AXIS AND DISPOSED BETWEEN A LIGHT SOURCE AND REGULAR PRISM ROTATING CONTINUOUSLY AT A RATE OF ONE PRISM FACET PER FRAME OF FILM, THE IMPROVEMENT RESIDING IN MECHANISM FOR REGULATING LIGHT INTENSITY AT THE APERURE AS CONSECUTIVE FRAMES ENTER, ARE EXPOSED AT AND DEPART FROM THE APERTURE COMPRISING: FIRST LIGHT-DIFFUSING MEANS MOVABLE IN PROGRESSIVELY INCREASING COVERING RELATION TO THAT PORTION OF THE APERTURE BETWEEN ITS FRAME-ENTRY EDGE AND SUBSTANIALLY ITS CENTER AND SAID MEANS BEING MOVABLE THENCE CLEAR OF THE APERTURE, SECOND LIGHT-DIFFUSING MEANS MOVABLE IN PROGRESSIVELY DECREASING COVERING RELATION TO THAT PORTION OF THE APERTURE BETWEEN SUBSTANTIALLY ITS CENTER AND ITS FRAME-DEPARTURE EDGE AND MOVABLE THEN CLEAR OF THE APERTURE, AND MEANS CARRYING SAID FIRST AND SECOND MEANS FOR SEQUENTIAL MOVEMENT AND IN SYNCHRONISM WITH FILM TRAVEL TO FOLLOW RESPECTIVELY ENTERING AND DEPARTING FRAMES, SAID FIRST AND SECOND MEANS BEING SO SPATIALLY RELATED THAT BOTH ARE CLEAR OF THE APERTURE AND THUS UNCOVER THE APERTURE FOR THE TRANSMISSION OF LIGHT AT HIGHER INTENSITY THAN THE DIFFUSED LIGHT UNDER CONDITIONS WHERE A FRAME IS CENTERED IN THE APERTURE AND WHERE ANY TWO CONSECUTIVE FRAMES ARE HALF-CENTERED IN THE APERTURE RESPECTIVELY AT OPPOSITE SIDES OF THE OPTICAL AXIS.