Lens Advantages

Performance

Canon Advantage - EF Lens Performance
STM Ultrasonic Motor EF Mount
Dust- and Water- Resistant Construction Fluorite/UD Elements Aspherical Elements
Diffractive Optics SWC Floating System
Circular Aperture Inner and Rear Focusing Focus Preset
AF Stop Feature Full-Time Manual Focusing Macro Shooting Mode

A challenge of shooting high definition video with EOS cameras has been achieving continuous autofocus. In response, new Canon EF, EF-S and EF-M lenses now offer a stepping motor (STM) drive, designed to deliver smooth and quiet continuous AF during video shooting when paired with the Movie Servo AF feature on select EOS cameras. Decades of proven optical expertise allow Canon to incorporate the right type of stepping motor for each lens. The EF 40mm f/2.8 STM utilizes a gear-type that allows the lens to achieve an ultra-compact and lightweight design; whereas the EF-S 18–135mm f/3.5–5.6 IS STM uses a lead-screw type, which prioritizes AF performance, offering the smoothest and quietest operation. The lightweight EF-M 18–55mm f/3.5–5.6 IS STM uses a lead-screw and rack type system, providing extremely quiet and smooth Movie Servo AF for optimal video shooting.

EF-S 18–55mm f/3.5–5.6 IS STM EF-S 18–135mm f/3.5–5.6 IS STM
EF 40mm f/2.8 STM EF-S 55–250mm f/4–5.6 IS STM
EF-M 18–55mm f/3.5–5.6 IS STM EF-M 22mm f/2 STM

Canon developed the world’s first lens-based Ultrasonic Motor (USM) to power the lens autofocus mechanism. Instead of large noisy drive trains powered by conventional motors, Canon USM lenses employ the minute electronic vibrations created by piezoelectric ceramic elements. The focusing action of the lens is fast and quiet, with virtually instantaneous stops and starts. USM lenses also draw minimal power from the camera, ensuring longer battery life. Canon makes two types of Ultrasonic Motor lenses. Ring-type USM lenses, found in large aperture and supertelephoto designs, permit manual focusing without first switching out of the auto mode. Micro USM designs bring the performance benefits of Canon’s USM technology to a wide assortment of affordable EF lenses.

In designing the EF and EF-M mount, Canon engineers gave photographers a lot more than a way to quickly attach a lens to a camera body. As the communication conduit between camera and lens, this fully electronic mount system has none of the shock, operational noise, abrasion, play, lubrication requirements, slow response, lever operation limitations or other design restrictions related to mechanical linkage mechanisms. A self-test system, using the lens’ built-in microcomputer, can even warn of malfunctions through the camera’s display. The EF and EF-M mounts enable high-speed autofocus, precise aperture control and preview, automatic compensation with lens extenders, and offer both forward and backward compatibility with lens technologies such as USM and Hybrid IS – and new optical designs as they are developed by Canon. Similarly, the EF-M mount, found on the EOS M Digital Camera, offers all the same communication points as the EF mount, and is compatible with all EF and EF-S lenses when used with an optional adapter.

Most L-series EF telephoto lenses are highly dust- and water-resistant thanks to rubber seals at the switch panels, exterior seams, drop-in filter compartments and lens mounts. Moving parts, such as the focusing ring and switches, are also designed to keep out environmental contaminants, providing reliable performance under harsh conditions.

Reducing color fringing, or chromatic aberration, has been one of the great challenges in the design of telephoto lenses. L-series telephoto lenses — like the EF 70–200mm f/2.8L II IS USM and EF 300mm f/4L IS USM — employ Canon’s Ultra-low Dispersion glass to minimize this effect, providing much improved contrast and sharpness. Even more effective at suppressing chromatic aberration are Fluorite elements, used in high-end supertelephoto L-series lenses. Although costly, a single Fluorite element has roughly the corrective power of two UD-glass elements, giving these L-series lenses their spectacular performance and relatively compact design.

Wide-angle lenses and fast normal-focal-length lenses often suffer from spherical aberration. When the light rays coming through the center of the lens do not converge at the same point as light rays coming through the lens edge, the image appears blurred because there is no sharp point of focus. Canon’s Aspherical elements use a varying curved surface to ensure that the entire image plane appears focused. Aspherical optics also help to correct curvilinear distortion as one might find in ultra wide-angle lenses. Finally, Canon can design aspherical elements with extremely precise variable curvature of one or both sides, making possible lighter and more compact lenses.

Canon’s use of diffractive optics (DO) results in high-performance lenses that are much smaller and lighter than traditional designs. Canon’s unique multilayer diffractive elements are constructed by bonding diffractive coatings to the surfaces of two or more lens elements. These elements are then combined to form a single multilayer DO element. Conventional glass lens elements disperse incoming light, causing chromatic aberration. The DO element’s dispersion characteristics are designed to cancel chromatic aberrations at various wavelengths when combined with conventional glass optics. This technology results in smaller lenses with no compromise in image quality. Canon has also developed a triple-layer type DO lens that uses an advanced diffractive grating to deliver excellent performance, with superior control of color fringing. This configuration is ideal for zoom lens optics and provides significant reductions in size. A good example is the EF 70–300mm f/4.5–5.6 DO IS USM lens, which is 28 percent shorter than the EF 70–300mm f/4–5.6 IS USM lens.

SWC is a proprietary lens coating that controls ghost and flare to a far greater degree than with earlier coating technologies. Utilizing SWC technology on large-curvature lens elements that are mainly found in wide-angle lenses will significantly minimize the occurrence of ghosting and flare caused by reflected light in environments that have posed problems. SWC is used on the Canon wide-angle lens, EF 24mm f/1.4L II USM.

Typical lenses correct for optical aberrations only at commonly-used focusing distances. Not surprisingly, at other focusing distances, especially close range, aberrations compromise image quality. Rather than using fixed spacings, Canon’s floating system dynamically varies the gap between key lens elements based on focusing distance. Aberrations are effectively suppressed throughout the focusing range, assuring high image quality in all shooting situations.

Canon lenses featuring circular aperture diaphragms employ curved blades to create a smoothly rounded opening as the lens is stopped down. As a result, out-of-focus background highlights are rendered as natural-looking rounded shapes rather than as distracting polygons. These lenses deliver smooth, consistent stop-down action (even at 10 fps), near-silent operation and excellent optical characteristics.

An inner focusing lens has the focusing lens group(s) in front of the diaphragm, while a rear focusing lens has the focusing lens group(s) behind the diaphragm. Both designs allow for compact optical systems that produce faster AF. And because the front of the lens does not rotate to focus, filter orientation remains constant.

Focus Preset enables you to program a focusing distance in the camera’s memory. Normal picture taking and focusing are unaffected by preset distances. For example, at a soccer game, you Focus Preset the goal area. Shoot normally elsewhere on the field, but once the action moves toward the goal, you can instantly return to the preset distance by turning a ring on the lens.

Pressing the AF Stop button (featured on several EF IS telephoto lenses) momentarily locks the AF to prevent the focus from shifting to a passing obstruction. After the obstruction has cleared, the focus will still be on the subject, and you can quickly resume shooting. AF Stop buttons are positioned at four locations around the lens grip for easy access.

Canon EOS cameras with EF lenses deliver impeccable AF precision. Manual focusing capability, nevertheless, can enhance flexibility. Canon EF lenses with full-time manual focusing enable the photographer to manually tweak focus without switching out of AF mode. Since AF action does not cause the focusing ring to turn, it can be made wider for improved grip and comfort.

The EF 24–70mm f/4L IS USM is a standard zoom that features a full-fledged Macro shooting mode. Setting the zoom ring to macro at the telephoto end enables close-up shooting possible at a minimum focusing distance of 0.66 ft./0.2m when set to macro, with a maximum magnification of 0.7x.