Effect similar to fluorite lens elements

The chromatic aberration correction effect is remarkable when a fluorite element is used. However, due to the high cost of fluorite compared to other materials, it cannot be employed widely on many lenses. To resolve this issue, Canon developed the UD (Ultra Low Dispersion) lens element, which is characterized by a low refractive index and low dispersive properties. It is widely employed in many lenses due to its ability to enhance the elimination of secondary spectrum.

Aspherical lens elements capable of converging light rays to a point

Traditional spherical lens elements are unable to ensure that light rays entering from the peripheral areas and those from the centre converge at the same point. Generally, it is difficult for spherical lens elements alone to correct spherical aberration on large-diameter lenses as well as distortion on wide-angle lenses. In contrast, aspherical lens elements have a lens surfacing with varying curvature, designed to make the light rays converge at the same. The manufacturing of aspherical lens elements requires a high level of processing technology and precise measuring techniques in order to produce a lens curvature for obtaining the ideal imaging point. Canon embarked on developing the technology for manufacturing aspherical lens elements at an early stage, and succeeded in 1971 in commercialising the world’s first lens with built-in ground and polished glass aspherical lens elements. Today, Canon has been able to contribute to enhancing the image quality of many EF lenses through the mass production of glass-mould and replica aspherical lens elements.

Enables silent and high-speed focusing

USM (Ultrasonic Motor) was first put into practical application in the world by Canon. USM drives the lens by transforming ultrasonic vibrations into rotation energy. Not only does it consume little power, it has high efficiency, torque and response, enabling high-speed focusing with almost no operating sound emitted.

There are three types of USM . The round-shaped Ring USM is simple in structure, and is best suited for use in a circular lens tube. It is especially useful for driving lenses such as large-diameter or super telephoto ones due to its high torque, and it also allows for full-time manual focusing. Meanwhile, the Micro USM can be employed on many types of lenses because it is low in cost and not subject to restrictions on the lens diameter. In 2002, Canon contributed further to the downsizing of lenses with the development of the Micro USM II, which is about half the size and weight of the Micro USM . And in 2016, Canon introduced Nano USM, which not only realizes a high speed AF that rivals that achieved by Ring USM, but also is able to operate quietly and seamlessly. It’s not an exaggeration to describe Nano USM as the most ideal motor for normal-use lenses that are meant to handle both still photography and movie shooting.

 Rung USM

Micor USM (Left), Micro USM II (Right)

Nano USM—The thin and tiny USM motor that achieves fast and smooth AF

Thin and compact, this USM, the latest to be developed by Canon, made its debut in 2016 on the EF-S18-135mm f/3.5-5.6mm IS USM. Computer chip-shaped (a factor that allows a more compact lens design) with power sources in the form of transducers, it connects directly to the AF actuating mechanism. It possesses a speediness and responsiveness that rivals that of the Ring USM, combined with a control that equals that of STM (lead screw-type). Its main benefit lies in enabling quiet, smooth AF operation in compactly-sized lenses such as standard zoom lenses. Also very suitable for movie-shooting, its high speed AF is able to handle scenes with subjects that are moving at a fast speed as well as those with unpredictable movements.

The Nano USM is shaped like a computer chip, and has 2 transducers in its center.

A cross section of the EF-S18-135mm f/3.5-5.6 IS USM, released in 2016 and the first lens to carry the Nano USM. Moving along the top of the slider, the Nano USM directly drives the main AF power source. As this motor not only allows for fast and smooth AF but is also small in size, it makes it possible for the lens that utilize it to be around the same size as lenses with STM.

Enables high-speed and precise AF

The inner focusing and rear focusing systems adjust the focus by moving only some of the lens elements inside the lens. Inner focusing refers to the type where the focusing lens group is located in front of the aperture diaphragm, while this group is positioned behind the aperture diaphragm in the case of the rear focusing type. As a smaller number of lens elements need to be moved, AF speed can be increased, and the size and weight of the entire lens can also be reduced. Besides, the front of the lens does not extend out during focusing, thus making it easy to achieve an integral lens structure, which in turn contributes to the enhanced robustness of the design. Yet another advantage of this system is that it enhances the operability of polarising filters as the filter mount does not rotate during focusing.

EF24-70mm f/2.8L USM Rear System                                  EF400mm f/5.6L USM Rear System

EF70-200mm f/2.8L IS II USM Inner System

Enables MF immediately after AF

Many of Canon’s EF lenses are equipped with “full-time manual focusing”, which allows manual focus right after auto focus is complete, just by turning the focusing ring and without the need to switch to MF mode. All Ring USM and STM lenses support full-time manual focusing.

Dust- and drip-proof for shooting under harsh conditions

Many of Canon’s L lenses come with a dust- and drip-proof structure, with rubber sealing applied to the interface area between the joint of the mount and the camera, as well as sealing at the movable parts such as the focusing ring and the lens extension tube. Rubber materials are also employed even at the smallest parts, such as the switch panel and the insertion slot of the drop-in filter compartments. The excellent dust- and drip-resistance enhances the usability of lenses under adverse weather, and helps to address the needs of professional photographers who are required to perform shoots under harsh shooting conditions. Fluorine-coated lenses allow dirt attached to the lens to be wiped off easily.

Minimises flare and ghosting substantially

SWC is the abbreviation of Subwavelength Structure Coating, a special coating technology developed by Canon to prevent the reflection of light rays. Reflection occurs due to the drastic change in refractive index when light passes through the boundary between the air and the glass surface. Reflection causes flare and ghosting, which in turn deteriorates the image quality. SWC removes the boundary plane that is subject to drastic changes in the refractive index by arraying on the lens surface countless wedge-shaped nanostructures smaller than the wavelength of visible light to change the refractive index gradually. It offers excellent anti-reflection effects for light coming in from different angles, ranging from those entering at an almost perpendicular angle to those with a large angle of incidence.

Anti-reflection theory of SWC

Powerful anti-reflection effect for perpendicularly-entering incident light

ASC is the abbreviation of Air Sphere Coating, the latest coating technology developed by Canon to effectively minimise the occurrence of flare and ghosting. Generally, multiple coating layers are applied to the lens surface to reduce light reflection at the boundary between the air and the lens surface. In the case of the ASC, a film consisting of silicon dioxide and air is applied over the usual vapour-deposition coatings to form an ultra-low refractive index layer. This film contains a certain percentage of air with a lower refractive index than optical glass, and helps to suppress light reflection. Compared to normal multi-layer coating, ASC is particularly effective for light that enters vertically as well as at high angles of incidence.

Anti-reflection theory of SWC

Expresses point light sources in beautiful round bokeh

The aperture is made up of several blades, the number of which determines the shape of the bokeh effect, such as in the case of illumination, light seeping through the leaves of a tree, and light reflection from the water surface. Light normally appears round when seen through our eyes, thus expressing light in a circular shape adds a more natural and soft touch to the resulting image. Almost all EF lenses employ a circular aperture diaphragm.