A picture showing the aperture and focus control rings. Notice the green A setting! In this mode, the camera controls a 9-blade aperture in the normal fashion. 4.5 to 6.7 is a stepless manual control for the 10-blade aperture. There are click-stops at A, 4.5, 5.6 and 6.7. The 4.5 and 6.7 apertures are perfectly circular. If you want a smaller aperture than 6.7, you will have to turn the ring back to A and set the aperture using the camera controls. This is awkward and slow.