The main requirement for a high-quality focal shutter is the stability of shutter speed and exposure evenness across the entire frame. The case where one side of the frame is exposed with a different amount of light than the other side is a common occurrence with a shutter failure. Classical asynchronous focal shutters especially suffer from this (for example, the shutters of the old Leica cameras).

So here’s the first feature: my new shutter has a rigid link between the first and second curtains, which form a gap for exposure. This slit does not change when moving along the frame window. The second feature is that my shutter curtains are noticeably longer than the classic curtains of other shutters, and the movement of the rigid gap starts noticeably earlier than the edge of the frame window, and the gap stops far beyond the frame border. That is, if in conventional shutters the curtains start moving and stop almost inside the frame, then in my shutter the curtains accelerate and slow down outside the frame. This feature ensures uniform movement of the slit along the entire frame.

These two features ensure the uniformity and stability of the exposure with a relatively simple shutter.

Another feature is a smooth change in the width of the gap between the curtains, which allows you to smoothly change the shutter speed. It’s not something special, it’s not an advantage over other types of shutters, but it’s just a nice feature. This capability is a side effect of the curtain’s rigid connection device.