Focusing means for a slide projector

Claim 1

IN A SLIDE PROJECTOR HAVING A SLIDABLY MOUNTED FORWARDLY AND REARWARDLY ADJUSTABLE LENS HOUSING WHEREBY TO PERMIT FOCUSING OF A PROJECTED IMAGE, THE IMPROVEMENT WHICH COMPRISES, A GEAR RACK FORMED ON THE SLIDABLY MOUNTED LENS HOUSING, A SHAFT ROTATABLY MOUNTED ADJACENT THE LENS HOUSING AND DISPOSED AT RIGHT ANGLES TO THE DIRECTION OF SLIDABLE MOVEMENT THEREOF, A PINION GEAR SECURED ON SAID SHAFT AND MESHED IN DRIVING ENGAGEMENT WITH THE GEAR RACK FORMED ON THE LENS HOUSING WHEREBY ROTATION OF SAID SHAFT IN OPPOSITE DIRECTIONS RESULTS IN FORWARD AND REARWARD FOCUSING ADJUSTMENT OF THE LENS HOUSING, ONE END OF SAID SHAFT EXTENDING EXTERNALLY OF THE PROJECTOR AND HAVING A KNOB THEREON TO PERMIT MANUAL FOCUSING ADJUSTMENT OF THE LENS HOUSING, A REVERSIBLE D.C. FOCUSING MOTOR, A GEAR TRAIN OPERABLY CONNECTED BETWEEN THE DRIVE SHAFT OF SAID MOTOR AND A GEAR ROTATABLY MOUNTED ON SAID SHAFT, A FRICTION CLUTCH INTERCONNECTING SAID SHAFT AND SAID GEAR WHICH IS ROTATABLY MOUNTED THEREON WHEREBY TO PERMIT BOTH MANUAL AND MOTORIZED FOCUSING ADJUSTMENT OF THE LENS HOUSING, AND CIRCUIT MEANS FOR SAID REVERSIBLE D.C. FOCUSING MOTOR INCLUDING CONDUCTORS CONNECTING AN A.C. POWER SUPPLY AND SAID MOTOR IN SERIES CIRCUIT RELATIONSHIP ACROSS A PAIR OF NORMALLY OPEN FORWARD AND REARWARD FOCUSING SWITCHES ARRANGED IN PARALLEL CIRCUIT RELATIONSHIP WITH EACH OF SAID PAIR OF SWITCHES HAVING A RECTIFIER ASSOCIATED THEREWITH, WHICH RECTIFIERS ARE CONNECTED WITH THEIR POLARITIES REVERSED, WHEREBY CLOSING THE FORWARD FOCUSING SWITCH ACTUATES THE FOCUSING MOTOR IN A DIRECTION OPERABLE TO SHIFT THE LENS HOUSING FORWARDLY AND CLOSING THE REARWARD FOCUSING SWITCH ACTUATES THE FOCUSING MOTOR IN THE OPPOSITE DIRECTION TO SHIFT THE LENS HOUSING REARWARDLY.