how do you cock the shutter in a wollensak dumont 75mm f1 9 oscilliscope lens? There is no way of cocking the shutter that I can see. I can see the blades. It looks as though it were half cocked. i like the wide aperture, just can't figure out how to make it work. Some guy on ebay has one for $2000, marked down to $1700. Go figure!???