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.

Silent and smooth AF

The STM (Stepping Motor) is an AF drive motor that is able to control the rotational operation of the motor using the fluctuation of pulse signals. Each electrical pulse signal can rotate the stepping motor by one step, and start-stop response is superb. The simple mechanical structure makes it easy to adopt a compact lens design. Also, the STM helps to reduce operating sound, and is thus ideal for video shooting. Canon developed two different types of STM according to the lens characteristics. The “STM + lead screw” unit adopts a lead-screw-type drive that is capable of generating a large torque, and enables silent and smooth AF drive on zoom lenses. The “STM + gear” unit allows for compact lens designs, and is optimised as a drive motor for compact lenses such as the pancake lens.

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.

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.