CAMERAS, CAMERA-STANDS, CAMERA-STAND JACKS, AND HOLDERS FOR SENSITIZED MATERIALSDRAEING, FOR CAMERAS, CAMERA-STANDS, CAMERA-STAND JACKS, TRIPODS, MULTIPLYING-BACKS FOR CAMERAS, PLATE-HOLDERS, NEGATIVE-RACKS; AUTOMATIC CABINET ATTACHMENTS, WHICH DEVICES TO FACILITATE FOCUSING AND MANIPULATION OF THE SENSITIVE PLATES IN PHOTOGRAPHIC CAMERAS; CURTAIN-SLIDE HOLDERS PROVIDED WITH CURTAIN-SLIDES; HEAD -SCREWS, HEAD-RESTS, BACKGROUND-BRACKETS,WHICH ARE DEVICES FOR SUPPORTING THE BACKGROUNDS IN SCENE...