Abstract: A masking apparatus and palpitator cone drive system for an X-ray spotfilming device. The masking apparatus comprises first and second pairs of shutter-like members mounted for reciprocating movement in two mutually orthogonal directions. Each mask member of the second pair includes first and second relatively moveable elements that operate in a telescope-like manner. A drive system including a reversible motor and a feedback potentiometer actuates the elements at first and second speeds so that the elements reach their retracted and extended positions simultaneously. The cone drive system includes a drive motor, a drive belt and drive assembly for driving the cone between retracted and operative positions. A cone lock is engageable with a keeper located at a cone-advanced position of the drive assembly and is released by the drive belt whenever the drive motor is energized in the cone-retracting direction.