It has only one effective aperture at any focal length, which varies from f/8.0 at 650mm to f/16.0 at 1300mm. That's not much of a hinderance, however, as you'd likely use this lens at its relatively small maximum aperture in any case. Only use this lens in fully manual mode or in aperture-priority autoexposure mode.
This lens requires bright light and high-ISO film to get a fast shutter speed, and needs a sturdy tripod or monopod, but can deliver very sharp results if used properly.