That is, a f/5.6 aperture value lets in twice as much light as does f/8. The difference between the two adjacent numbers is called one stop. A f/16 value is one stop larger than f/22. "Opening" the aperture means making the aperture larger. "Closing" or "stopping down" means making it smaller. It should be noted here all the Canon EF lenses introduced for use with the EOS 35mm AF SLR cameras do not have any aperture ring in contrast to the manual focus FD lenses for use with the discontinued series of manual focus Canon 35mm SLR cameras. All EOS cameras controls the aperture settings with the Main Dial (AE modes) or using the Quick Control Dial or the combination of both the Exposure Compensation button with the Main Dial when used in the Manual Exposure mode. The Electro-Magnetic-Drive (EMD) aperture blades in every EF lenses made it possible for the EOS cameras to control the aperture settings from the camera body. This feature is another benefit of the fully electronic lens mount used in the Canon EOS series. << Back to Main . 1 . 2 . 3 . 4 . 5 . 6 . 7 . 8 . 9 . 10 . 11 .