The shutter consists of a cylinder and piston attached eccentrically to a plate which in turn is attached to a coiled spring. The piston is attached to the plate by a short pin which also travels in a cut-out of the shutter plate. The arrangement is such that when released the spring rotates the plate and in turn the cylinder and piston. As the piston rotates so the shutter plate is caused to move upwards by the movement of the pin within the slot. For some distance the movement is quite free, later the pin reaches the end of the slot and its movement is resisted. This causes the piston to slide within the cylinder which forms a normal pneumatic delay. At its furthest point of travel the piston and cylinder starts the return to its initial position and the shutter plate is also brought down. On its return the pin is still guided within the slot and in order to move, the piston has to travel out of the cylinder, again causing a delay. After a time movement becomes free and the shutter, piston etc. moves quicker.

The important point is that movement is free and therefore quick at the start and end of the exposure, the time delay occurs whilst the lens is fully uncovered. The shutter was also sold under other names.

The illustration at a) shows the shutter blade covering the lens, the circular plate carrying the piston is starting to revolve lifting the plate. At b) the plate is nearly lifted, free movement of the pin is restricted so the piston is forced into the cylinder. At c) the blade is fully lifted and the piston is fully within the cylinder. The blade now starts its return.

These were often known as drop or elastic-band shutters. A blade, usually of vulcanite or wood, is held over the lens against an elastic-band. When released the blade rises, the movement dislodges the elastic-band allowing the blade to drop back and cover the lens.