Graflex used a moving slit curtain. The slit was fixed sizes. It is one moving curtain, not two independent curtains.
Originally Posted by Bill Burk
Lens shutter solves the problem only if that shutter supports X-synch. Many, if not most, do but there were some shutters that did not have synch except that improvised using a solenoid... and that can't fake a X-synch.
EDIT: what Serius refers to as "O" setting on the Graflex focal plane shutter is FULLY OPEN - meaning the opening is 4 inches on a 4x5 camera. That is not a shutter speed setting, per se, but a way to keep the focal plan shutter curtain out of the way when using a lens shutter.