Focal-plane Shutter - The Rotary Focal-plane Shutter

The Rotary Focal-plane Shutter

Besides the horizontal Leica and vertical Square FP shutters, other types of FP shutters exist. The most prominent is the rotary or sector FP shutter. The rotary disc shutter is common in film movie cameras, but rare in still cameras. These spin a round metal plate with a sector cutout in front of the film. In theory, rotary shutters can control their speeds by narrowing or widening the sector cutout (by using two overlapping plates and varying the overlap) and/or by spinning the plate faster or slower. However, for simplicity's sake, most still camera rotary shutters have fixed cutouts and vary the spinning speed. The Olympus Pen F and Pen FT (1963 and 1966, both from Japan) half frame 35 mm SLRs spun a semicircular titanium plate to 1/500 sec.

Semicircular rotary shutters also have the advantage of unlimited X-sync speed, but all rotary FP shutters have the disadvantage of the bulk required for the plate spin. The Univex Mercury (1938, USA) half frame 35 mm camera had a very large dome protruding out the top of the main body to accommodate its 1/1000 sec. rotary shutter. They also produce very unusual distortion at very high speed because of the angular sweep of the exposure wipe. Bulk can be reduced by substituting blade sheaves for the plate, but then the rotary FP shutter essentially becomes a regular bladed FP shutter.