I wasn't thinking about mechanical shutters per se. I was thinking about exposure control. So shoot me for implying you could set a half-speed on a mechanical shutter.

Again, not having shot with a C2xx/3xx Mamiya, I'm not familiar with the specifics of aperture/shutter speed settings for their lenses, so you'll forgive me for suggesting some combination of settings that are not available on that specific piece of gear. As I already noted, you'd be lucky to be able to set anything other than half-stops for aperture settings, so the greatest precision you'd have would be 1/2 stop. More precise than 1/2 stop you'd not be able to detect in a print, and even with a chrome you'd have a hard time seeing a 1/4 stop difference.