Registration method and frame

Claim 1

IN A PHOTOGRAPHIC PROJECTOR OF THE TYPE INCLUDING A PLATFORM HAVING A RECTANGULAR LIGHT TRANSMITTING OPENING THERETHROUGH, A FRAME FOR SUPPORTING AND REGISTERING FLAT TRANSPARENT RECTANGULAR SHEETS OVER SAID OPENING, SAID FRAME BEING RECTANGULAR AND HAVING A RECTANGULAR OPENING TO REGISTER WITH SAID OPENING IN SAID PLATFORM AND BORDERED BY A FLANGE TO SUPPORT SUCH SHEETS, A PLURALITY OF SHEETS SET ON SAID FLANGE IN OVERLYING RELATION TO SAID OPENING IN THE FRAME, EACH OF WHICH SHEETS HAS TOP AND BOTTOM PARALLEL EDGES AND PARALLEL SIDE EDGES PERPENDICULAR TO SAID TOP AND BOTTOM EDGES AND ALSO HAS A PLURALITY OF NOTCHES IN ONE EDGE SPACED DIFFERENTLY FROM THE CORRESPONDING EDGES THAT ARE PERPENDICULAR TO SAID ONE EDGE SAID FRAME ALSO HAVING GUIDE ELEMENTS THEREON SPACED FROM THE EDGES OF SAID OPENING IN THE FRAME EACH TO ABUT ONE END OF SAID SHEET, ONE OF SAID GUIDE ELEMENTS COMPRISING A PLURALITY OF LUGS SPACED FROM EACH OTHER ALONG ONE EDGE OF THE OPENING IN THE FRAME A DISTANCE CORRESPONDING TO THE DISTANCE BETWEEN SAID NOTCHES IN THE SHEET, EACH TO ENGAGE ONE OF SAID NOTCHES FOR REGISTERING THE SHEETS RIGHT SIDE UP WITH SAID OPENING IN THE FRAME.