July 2010

History of the EF Lens

In celebration of our 50 millionth EF lens

In celebration of our 50 millionth EF lens

In this month’s technical report, we review the history of the EF lens in celebration of the 50 millionth EF lens, which was produced last December.

The EF lens and its all-electronic mount pave the way for genuine autofocus functionality and anticipate today’s digital era

The first EF lens was introduced in 1987, debuting alongside the EOS camera. Breaking with the previous FD mount, the EF lens mount was designed to bring genuine autofocus (AF) functionality to SLR cameras. It was revolutionary. Its forward-looking design anticipated today’s digital photo era more than 20 years ago.

The hardest decision at the time was to take the plunge and change the lens mount. The previous FD mount had won the absolute trust of professional and amateur photographers. Despite this, Canon used a radically different, all-electronic mount*1 for EF lenses and EOS cameras.

What differentiated the EOS’s AF system was the in-lens motor*2 — that is, the focusing mechanism’s drive motor was placed inside the lens. Most other AF SLR systems housed the drive motor in the camera body, which necessitated mechanical linkages — shafts or levers — through the mount mechanism to adjust the focusing lens group. Canon’s decision to employ in-lens motors was based on the approach of placing optimized drive sources near their corresponding drive mechanism. Since the in-lens motor was specifically designed for the lens’s particular focusing lens group, it achieved faster AF drive speeds.

Canon’s AF drive was not only faster, it was quieter too because Canon was the first camera maker to use ultrasonic motors (USM)*3 in its lenses. Newly developed at the time, a USM converts ultrasonic vibrations into rotational movement. “Fast and comfortable” — the slogan used during the EOS 650 launch — neatly sums up the benefits of the USM, which pairs high torque with excellent starting and stopping characteristics.

The new EF mount led to a series of developments. Besides AF functionality, it enabled several automatic photographic functions due to its all-electronic configuration. The Canon AE-1, an entry-level SLR, was a huge hit in the 1970s because of its auto exposure (AE) feature. Following this success, Canon developed an electromagnetic diaphragm (EMD) unit,*4 which used a motor to control the aperture blades with great precision. This development led to the advent of AE control without mechanical linkages.

Advances in automatic features reduce the number of wasted shots

Generally speaking, the three major causes of flawed photos are poor exposure, poor focus, and camera shake. Canon embarked on a mission to resolve each of these through technology. Therefore, the next step for Canon was to add image stabilization (IS)*5 to EF lenses.

IS first appeared on the market some eight years after the EF mount debut. This single development made telephoto shooting, which had presented a steep learning curve for amateur photographers, suddenly much more accessible.

The most recent IS technology — Hybrid IS*6 — appeared in 2009. Hybrid IS solves camera shake problems experienced in close-up photography. This technology is able to detect and compensate for lateral shake, a phenomenon that occurs when the camera moves in a planar direction to the subject during macro photography.

The lens and body must transmit a large amount of information back and forth in order to realize new technologies such as Hybrid IS. One reason for moving to an all-electronic mount was the flexibility to add new technologies in the future as they emerge. The correctness of this approach has been validated with each new functional breakthrough, such as the first IS system incorporated into a 35mm SLR interchangeable lens and one-touch exposure simulations that stop down the aperture when using Live View shooting on a digital SLR.

The L series zoom lenses offer a new style of pro equipment

Prior to FD lenses, professional photographers who embraced zoom lenses were few and far between. Most photographers were firm believers in prime lenses only. Thus, it was a given in the industry to see pros cart around a full slate of prime lenses from wide angle to telephoto. With the introduction of the legendary FD 35–70mm f/2.8–3.5 SSC and FD 80–200mm f/4 SSC zoom lenses however, professional photographers gradually became more accepting of zooms.

In conjunction with the release of the first pro body, the EOS-1, in 1989, Canon marketed three L (for Luxury)*7 zoom lenses — the EF 20–35mm f/2.8 L, the EF 28–80mm f/2.8–4 L USM, and the EF 80–200mm f/2.8 L — as “everyday” pro lenses. These three zooms covered the focal length range of about 10 prime lenses. This also ushered in a new style of professional equipment. Of course, it was only possible to make these L series zooms because pros had recognized the zoom lens technology developed and refined in the FD lens era.

Amateurs, on the other hand, found zooms extremely attractive. Not only were they easy on the pocket book, zooms allowed amateurs to choose the angle of view at will with just one lens, made travelling light a snap, and offered zooming that was fun in itself. In a very real way, zooms gave beginners an opportunity to actively explore photography.

The concept behind the first three L zooms soon became entrenched, and our current f/2.8 L zoom lenses — the EF 16–35mm f/2.8 L II USM, the EF 24–70mm f/2.8 L USM, and the EF 70–200mm f/2.8 L IS II USM — have carried this concept forward.

As more seniors become photo enthusiasts, there are increasing calls for lighter high-performance lenses. The f/4 L series was developed in response to these demands. The first in this series was the EF 70–200mm f/4 L USM, but it was joined by a succession of other lenses — the EF 17–40mm f/4 L USM, the EF 24–105mm f/4 L IS USM, and the EF 70–200mm f/4 L IS USM. The L brand’s legacy is probably why these four new zoom lenses have won over so many pros and advanced amateurs.

Answering dreams with TS-E and other highly specialized lenses that open up new creative photographic possibilities

To support everyone’s photographic expectations, Canon does more than just build best sellers. Canon is committed to offering products that fulfill even niche demands.

A good example of this approach is the TS-E series. These are highly specialized perspective-control lenses*8 for 35mm cameras. Perspective control is a general name for both shift and tilt controls. Shifting moves the lens surface, which is typically positioned at the front of the bellows on a large-format camera, parallel to the image plane. What this accomplishes is to correct converging parallel lines in an image, such as what happens when shooting a tall building from ground level. Tilting controls the plane of sharp focus by changing the angle between the optical axis and the image plane. Because tilt and shift control is frequently required in architectural and product photography, our TS-E lenses are prized for making these types of shots possible despite their smaller 35mm size.

Due to recent advances in the resolution and image quality of digital SLR sensors, 35mm digital is gradually replacing medium-format and large-format cameras for tilt-shift photography. Because of this, 35mm has already become the format of choice in the product photography field. Thus, the availability of TS-E lenses for photographers has made significant changes in certain aspects of the photography industry.

Our EF macro lens — with the long-winded name of MP-E 65mm f/2.8 1–5x Macro Photo — replaces bellows systems, which are a chore to carry and difficult to operate. This macro lens is also special in that it only enlarges subjects, between 1x and 5x, and doesn’t focus at normal shooting distances. This single lens, when combined with a digital SLR, is designed to open up new creative possibilities with the allure and excitement that those possibilities provoke.

Continually evolving EF lenses accelerate new photography delights unveiled by the move to digital

Everyone watching the migration from film photography to digital was excited about the dramatic changes to camera bodies.

Since entering the 21st century, however, many people have been using computers to examine their digital photos at extreme magnifications and have become much more critical about lens characteristics — such as resolving power*9 and chromatic aberrations*10 — that previously did not cause much concern. On the flip side, the increased scrutiny has meant that more people, and not just professionals, now understand the superiority of EF lenses, which resulted from Canon’s sweeping revisions to improve optical characteristics and remedy the concerns.

L lenses have been recognized for their superlative image quality since the film days, but people with few chances to make large prints were unable to sense the level of quality these lenses can deliver. But thanks to the digital era and the rapid increase in sensor resolutions, even ordinary users can now confirm with their own eyes the image sharpness and other rendering qualities of L lenses. Consequently, L lenses are rated higher than ever before.

Optical design has continued to evolve in many ways since the onset of digital photography even though exterior appearances have changed only slightly. These advancements include switching to a rear-focus design*11 for better AF performance and reducing the optical system’s weight to improve the handling characteristics with IS.

More recently, we have worked to reduce reflections*12 that occur within a lens, which causes ghosting,*13 with a special new coating called SWS.*14 SWS uses nano-structures and nano-fabrication technology.

Canon continues to invest in many research fields with the objective of creating products that deliver more satisfaction to more people.

*1 All-electronic mount

The fully electronic mount eliminates all mechanical linkages between the body and lens. Instead, it uses bidirectional digital communications to transmit information between the lens and the body. Information includes the type (ID), maximum aperture, present focal length, extension, and other information about the lens. Because all information is communicated electronically, the mount can be easily adapted to support new lens technologies and improved camera specifications.

All-electronic mount

*2 In-lens motor

The AF drive motor is built into the lens. This design embodies Canon’s basic approach of placing optimized actuators (drive sources) near their drive mechanism and implementing all data communications and control electronically. This approach has solved previous drive inefficiencies that resulted when a single motor in the camera body had to support all interchangeable lens types (the focus torques of which varied by as much as 10 times).

*3 Ultrasonic motor (USM)

A USM converts ultrasonic vibrations into rotational energy. USMs are used to realize quick, silent autofocusing. With the EF lens, Canon was the first in the industry to successfully use USMs in commercial lenses. Another first in 1987 was the ring-type USM for telephoto lenses. Canon also developed the cylindrical Micro USM in 1992 and the Micro USM II in 2002, which was about half the size of the original Micro USM.

Ultrasonic motor (USM)

*4 Electromagnetic diaphragm (EMD) unit

This unit combines the stepper motor and the aperture blade assembly. This unit is used in keeping with the all-electronic mount concept, because it can control the aperture diameter with electronic signals.

Electromagnetic diaphragm (EMD) unit

*5 Image stabilizer (IS)

The EF lens was the first 35mm SLR interchangeable lens with a built-in IS unit. The IS unit allows a section of the optical system to shift up and down parallel to the optical axis. In this way, the unit corrects images for angular shake, which occurs when the lens moves with the camera body as the pivot point. Angular shake has a big impact on ordinary shots.

*6 Hybrid IS

Hybrid IS is the very latest IS technology. In addition to regular angular shake, it compensates for lateral shake — which occurs when the camera moves in a planar direction with respect to the subject — which poses a problem for macro photography. Hybrid IS debuted on the EF 100mm f/2.8 L Macro IS USM lens in 2009 and is the industry’s first IS system that simultaneously corrects two types of camera shake.

Hybrid IS

*7 L series lenses

L stands for Luxury. This lens series features professional image specifications and employs special optical materials such as synthetic crystalline fluorite elements, ultra low dispersion (UD) elements, and super UD elements, and precision, large radius aspherical elements. L lenses combine superlative performance with superb ruggedness and durability.

*8 Perspective-control lenses

Perspective control refers to shift — which corrects image deformations by moving the lens optical axis parallel to the image plane — and tilt — which adjusts the plane of sharp focus by changing the parallel relationship between the lens optical axis and the film surface (image plane). Perspective control was traditionally done with large-format cameras, but today’s lenses give perspective control to 35mm cameras.

Perspective-control lenses

*9 Lens resolving power (resolution)

A measurement of lens quality that expresses a lens’s ability to exactly reproduce the subject’s point image.

*10 Chromatic aberrations

Ordinary light is a mixture of many colors. The refraction index of light varies according to its color, or more specifically to its wavelength. Thus, the image forms in a slightly different position depending on the color. This phenomenon is known as color fringing. Chromatic aberrations are corrected by combining a convex lens and a concave lens with different refractive indexes to cancel the aberrations out. The strength of chromatic aberrations is further reduced with fluorite elements, (UD) elements, and super UD elements, which have very low optical dispersion indexes.

*11 Rear-focus design

In this lens arrangement, the lens group next to the (rear) image plane and behind the aperture is adjusted to bring the image into focus. The advantages of rear focus are a more compact lens, superior handling balance, and a lighter focusing lens group for faster and more accurate AF control.

Rear-focus design

*12 Ghosting

When a bright light source like the sun enters the image frame, it causes complex reflections at the lens surface and sometimes imprints a reflection in the opposite position from the light source. This phenomenon is called ghosting because the reflections look spooky.

Ghosting

*13 Light reflections within the lens (flare)

Light reflected off the lens surface or off the inner wall of the barrel or the camera’s mirror box sometimes reaches the image plane causing a loss of image sharpness in part or all of the frame. This destructive reflected light is called flare.

*14 SWC coating

SWC stands for subwavelength structure coating. This technology gives superior anti-reflective performance even when light strikes the lens at a large angle of incidence, which conventional coatings cannot control. SWC is an arrangement on the lens surface of countless conic nanostructures that are shorter than the wavelength of visible light.

SWC coating