More than seven decades after our first lens breakthrough, innovating the world of optics remains a singular focus for Canon engineers. Here you’ll find just some of the advances that have resulted in crisper, clearer images, quieter, more durable gear, and ultimately, more freedom for photographers and cinematographers everywhere.
Light rays entering at the edges of spherical lens elements converge at slightly different focal points to light rays entering from the center. Known as spherical aberration, this optical phenomenon produces soft, low contrast images that look as if covered with a thin veil.
Canon developed aspherical lens elements to counteract this problem. A special non-spherical surface converges central and peripheral light rays at a single focal point to help ensure uniform sharpness and clarity over the whole image area. Now found in a wide variety of EF lenses, aspherical lens elements are particularly useful for large-aperture lenses, wide-angle lenses and high quality compact zoom lenses.
Canon developed the world’s first lens-based Ultrasonic Motor (USM) to drive autofocus for instant response. Instead of conventional motors that add weight and noise, Canon’s USM technology uses miniscule electronic vibrations for fast focusing action with virtually instantaneous stops and starts. USM-powered lenses also draw minimal power from the camera, helping to ensure
longer battery life.
Ring-type USM technology, found in large aperture and super telephoto EF lenses, allows filmmakers to manually focus without first switching out of the auto mode. Here, autofocus is almost silent, and the focus ring allows you to manually override focus in an instant.
When a lens vibrates through unintended camera movement (such as a shaky hand when rack focusing), incoming light rays are shifted, resulting in an unsteady image. Canon Image Stabilizer (IS) technology uses a lens shift-type system to detect and help correct these slight camera shakes.
IS begins working when minute gyro sensors detect lens vibrations and send a signal to a microcomputer. This microcomputer controls an IS lens group that compensates for the movement along the horizontal and vertical axis of the camera/lens. Canon IS also assists photographers when hand-holding telephoto lenses. The use of a tripod becomes less necessary when shooting at slower shutter speeds with Canon IS.
The operating noise of a lens during autofocus can be obtrusive, especially when shooting video. To help minimize this sound, Canon employs an STM (stepping motor) in some of its EF lenses. Designed to operate in synchronization with pulsed power, the STM rotates a single step per pulse of electrical signal. Accordingly, STMs, which are also known as pulse motors, offer superb response and controllability at start and stop. Their simple mechanical structure also contributes to smooth, low-noise lens operation and smaller lens sizes.
Fluorite and UD Lenses
If you hold a prism up against sunlight, a rainbow spectrum will appear. This is due to the fact that different wavelengths of light refract—or bend—at different points within the prism. The same phenomenon occurs to a lesser degree in photographic lenses, where it’s known as chromatic aberration. This is most noticeable in photographs as color fringing at the edges of objects. Combining convex and concave lenses helps to correct the problem but does not entirely resolve it.
Fluorite, which boasts a very low dispersion of light, is capable of combating the residual aberration that standard optical glass fails to eliminate. Canon succeeded in artificially creating crystal fluorite in the 1960s, producing the first interchangeable SLR lenses with fluorite elements. In the 1970s, Canon achieved the first UD (Ultra Low Dispersion) lens elements incorporating low-dispersion optical glass. This technology was further improved to create Super UD lenses in the 1990s. Combinations of fluorite, UD and Super UD elements are used in many of today's L-series super-telephoto lenses, telephoto zooms and wide-angle lenses.
Full-Time Manual Focus
While autofocus can often save time and improve focusing accuracy, there are still creative choices photographers and cinematographers can make to further craft and control the visual elements in a shot. Many Canon EF lenses are equipped with a ring-type USM that allows full-time manual focus, even when the AF/MF switch is set to autofocus. This enables manual tuning of focus as soon as autofocus is complete, without the need to switch to manual focus mode. Full-time manual focus is also possible on some lenses equipped with a Micro USM, such as the EF 50mm f/1.4 USM.
EMD (Electromagnetic Diaphragm) is a diaphragm drive control actuator—a component that integrates both a stepping motor and a diaphragm blade unit in a single unit—using fully-electronic data transmission in the EF mount system. EMD utilizes a stepping motor and diaphragm blades to control aperture diameter by means of electronic pulse signals from the camera body. This reduces lag time between shutter release and aperture control, while helping to increase reliability, making EMD lenses much more consistently accurate than optics with conventional mechanical linkage systems. Every EF lens incorporates an EMD unit as a basic component of the EOS system.
Super Spectra Coating
When light waves enter an uncoated lens, four to ten percent of that light is reflected off the surface of each of the internal lens elements. This reflected light, if not dealt with properly, can reduce overall light transmission and contaminates black reproduction by
flare and veiling glare.
Canon’s multi layer Super Spectra coating allows up to 99.9% of light to emerge from each lens element. This considerably increases the amount of light reaching the camera’s CMOS sensor while also helping to minimize the effects of ghosting and flare, and helps ensure a consistent color balance that plays a key part in delivering the sharp, high-contrast results that all Canon lenses are renowned for.
Light travels in waves, which enter your lens at different speeds or wavelengths. Because of this, conventional glass lenses often bend certain waves of incoming light, causing chromatic aberration, or color fringing. Diffractive optics (DO) are designed to block the unnecessary, diffracted light that mars your image with color fringing. Employing multiple DO elements helps ensure that nearly all light allowed to pass through the elements can be used for photography.
Canon DO lenses use multiple elements featuring diffractive gratings bonded face-to-face. Combining this arrangement with a refractive convex lens almost completely cancels out chromatic aberration while allowing the lens elements to be placed much closer together within the lens barrel. The result is a high performance EF lens that's significantly shorter and lighter than typical refractive lenses.