In a old LF Fujinon lens catalog, there is a table mentioning that Fujinon SWD and SW lenses are mounted in #00 shutters, which have a 18mm max aperture diameter. Usually, I read that Seiko or Copal shutters do not exist in #00.
But they do !
At least Seiko did #00 shutters, I have one on an old SWD 5.6/65mm.
It is actually exactly the same shutter as a #0, but the shutter blades do not open completely ! They are stopped at around 20mm diameter, it is obvious when the front lens is removed, but not visible otherwise. Aperture opens completely however.
This is an interesting adaptation. I would venture that it makes the shutter speeds more accurate at high speed since they don't have to travel as far, as it is not needed.
I think they changed this to rationalize the production; not sure the improvement in speed made such a big difference between a #00 and a #0 to motivate two different productions. Not to mention the head scratching when mounting a lens requiring a #0 on a #00 shutter and seeing the shutter blades sticking out!
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