A photographic copying machine wherein any one of a series of masks, each having a differently dimensioned light-transmitting opening, can be placed onto a locating plate which supports a battery of fixedly mounted or mobile magnetic actuators for discrete electric switching elements. Each mask carries a different array of soft magnets which displace or otherwise influence a group of actuators so that the thus influenced actuators open or close the associated switching elements which adjust the exposure controls and/or another system of the copying machine in dependency on the size and/or shape of the opening in the selected mask. The soft magnets on each mask influence a different group (e.g., a different number) of actuators each of which is an H-shaped permanent magnet.