A shutter release cable adapter for connection to a mechanical shutter release of a film camera is provided with a bi-stable magnetic device to selectively position an internal shutter release plunger to either a translation blocking or unblocking position depending on an operating condition of the image capture system of which the film camera is a part. The magnetic device includes an electromagnet responsive to a system condition signal to generate a reversible magnetic field and a permanent magnet interactive with the electromagnetic field to position a projection mounted on the internal plunger to the respective blocking or unblocking position as determined by the condition of the image capture system. In the absence of an electromagnetic field the permanent magnet retains its assumed position by attraction of the permanent magnet field to the armature poles of the electromagnet.