Canon ef 70-200mm f/4l is usm lens offers the highest possible optical quality with no change in aperture over the full focal range of the lens. This allows photographers to set exposure at the widest aperture and zoom all the way through to 200mm without having to decrease shutter speed. Developed for use with a canon slr camera, this autofocus telephoto zoom lens offers optimized use with the canon eos series digital cameras. Of particular note, canon has introduced an image stabilizer (is) that adjusts to meet the demands of professional photography. Is reduces dramatically the image blur caused by camera shake. Gyro sensors detect unwanted vibrations, triggering the corresponding movement of a correcting lens group perpendicular to the optical axis. This alters the light path, returning the image to its correct position on the sensor or film plane. For shooting immobile subjects, mode 1 corrects for movement in the image along both the horizontal and vertical axes. For shooting while panning horizontally to follow a moving subject, mode 2 turns off vertical correction and prevents the effect of dragging the subject back through the frame. The lens' ring-type usm employs ultra-sonic frequency vibrations to drive auto focus with unrivalled speed and near-silent operation. A powerful cpu and improved af algorithm contribute to speed performance.