Image Stabilizer IS dramatically reduces image blur caused by camera shake. The EF 70-300mm f4-5.6 IS USM features Canon's latest 3-stop IS, a one-stop improvement over its predecessor. This allows shutter speeds up to three stops slower than would otherwise be possible, with no perceptible increase in image blur. Photographers normally shooting a 300mm frame handheld at 1/500 second can obtain the equivalent result with a shutter speed of just 1/60 second, vastly extending options in low-light conditions. 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. The EF 70-300mm f4-5.6 IS USM provides 2-mode IS for shooting immobile subjects. Mode 1 stabilizes the image along both the horizontal and vertical axes. For shooting while panning to follow a moving subject, Mode 2 turns off correction in the panned direction and prevents the effect of dragging the subject back through the frame. IS switches off automatically when the camera is mounted on a tripod, thus preventing feedback loops between the IS sensor and stabilizer motor vibrations.
Superb Autofocus The micro USM motor found in the EF 70-300mm f4-5.6 IS USM employs ultra-sonic frequency vibrations to drive auto focus with unrivalled speed and near-silent operation. Good holding torque stops the lens with precision and accuracy, the instant it arrives at the correct focus point and without overshoot. A high-speed CPU and optimised AF algorithm result in a significant increase of AF speed compared to that of its predecessor. A zoom ring locking mechanism is provided that locks the zoom at the wide-angle setting. This ensures that the lens is carried or stored in its most compact position, preventing possible damage caused by the lens extending and hitting obstacles when being carried mounted on a camera with a strap.
Pleasing defocused background The EF 70-300mm f4-5.6 IS USM employs an electro-magnetic diaphragm (EMD) with a circular aperture. This helps create an attractive, even defocused background when isolating a subject at large apertures.
Image Quality By optimizing Super Spectra lens coatings and lens element shaping, Canon's engineers have been effective in suppressing flare and ghosting--more prone to occur with digital cameras due to reflection off the image sensor. By increasing light absorption, coatings reduce reflections off lens element surfaces to deliver crisp, undistorted images with natural color balance.