Shutters are manufactured to accommodate different lenses. Most 90mm f/8 lenses don't require as large a maximum aperture as these shutters. There's no real need to block the shutter from opening more than enough for whatever lens is installed in the shutter. You can easily check the aperture scale by measuring the apparent diameter of the aperture opening as seen through the front lens cell. Don't get your eye really close to the lens while doing this to avoid a parallax error. The apparent diameter of the aperture should be 11.25mm at f/8. An error of a millimeter or so will cause little exposure error.