The Olympus PEN cameras (and subsequent small cameras by olympus) have a in lens shutter that is simply two blades. The blades have a triangle cut out of each s

The Olympus PEN cameras (and subsequent small cameras by olympus) have a in lens shutter that is simply two blades. The blades have a triangle cut out of each side and form a diamond shaped aperture. In this shutter the shutter blades form the aperture. This design is from at least 1959 with the release of the PEN.