Illumination control system

Claim 1

IN A RECORDING APPARATUS OF THE TYPE IN WHICH A DOCUMENT TO BE REPRODUCED IN PROJECTED IN LINE SCAN FASHION ONTO A PHOTORECEPTOR MOVED PAST AN EXPOSURE STATION CHARACTERIZED BY AN ILLUMINATION CONTROL SYSTEM COMPRISING IN COMBINATION: SUPPORT MEANS LOCATED AT THE OBJECT PLANE TO POSITION A DOCUMENT TO BE REPRODUCED, A SOURCE OF ILLUMINATION OPTICALLY POSITIONED TO ILUMINATE THE DOCUMENT, A PHOTORECEPTOR AT THE IMAGE PLANE TO RECEIVE A PATTERN OF LIGHT AND SHADOW ACCORDING TO THE DOCUMENT TO BE RECORDED, AN OPTICAL SYSTEM TO PROJECT A LINE SCAN IMAGE OF THE DOCUMENT ONTO SAID PHOTORECEPTOR, SAID OPTICAL SYSTEM INCLUDING A SPHERICAL LENS CORRECTED FOR OBLIQUE SPHERICAL ABERRATION IN THE TANGENTIAL PLANE, LIGHT MASKING MEANS INTERPOSED IN THE OPTICAL PATH IN CLOSE PROXIMITY TO SAID LENS INCLUDING A PAIR OF SPACED APART WALL MEMBERS IMPREVIOUS TO LIGHT ADAPTED FOR MOVEMENT TRANSVERSE TO THEE OPTICAL CENTER LINE IN THE SAGITTAL DIRECTION TO MASK OUT SELECTED LIGHT RAYS, DRIVE MEANS OPERATIVE TO POSITION SAID WALL MEMBERS TOWARD AND AWAY FROM THE OPTICAL CENTER LINE TO CONTROL THE INTENSITY OF ILLUMINATION AT THE SURFACE OF SAID PHOTORECEPTOR AT A PREDETERMINED LEVEL IN RESPONSE TO DISCRETE BI-POLAR ELECTRICAL SIGNALS, CIRCUIT MEANS COUPLED TO SAID DRIVE MEANS TO EMIT DISCRETE BI-POLAR ELECTRICAL SIGNALS TO ACTUATE SAID DRIVE MEANS TO MOVE SAID WALL MEMBERS TOWARD AND AWAY FROM THE OPTICAL CENTER LINE IN A SAGITTAL DIRECTION TO MAINTAIN A PREDETERMINED LEVEL OF AN ILLUMINATION ON THE SURFACE OF SAID PHOTORECEPTOR WITH A MINIMUM OF OPTICAL DETERIORATION THEREAT.