The World of L-series LensesTechnology

Fluorite

Fluorite is an amazing mineral that emits and disperses light when heated to high temperatures. The stone was named “fluorite” for its beauty and fluorescent properties. Calcium fluoride (CaF2) is a naturally occurring crystalline mineral. When made synthetically, calcium fluoride crystals have outstanding optical characteristics including low dispersion, an extremely low refractive index, and excellent transmittance of infrared and ultraviolet light. Most importantly, fluorite can produce clear, detailed image delineation that conventional optical glass simply cannot match. Canon set out to leverage these properties when it inaugurated the “F” Program, to develop high-performance camera lenses incorporating fluorite.

Fluorite had been a focus of attention for centuries. In the 1800s, natural calcium fluoride crystals were already being used as objective lenses in microscopes. Later, attempts were made to produce synthetic fluorite crystals for use as lenses in larger instruments such as telescopes. However, technical hurdles were high and many believed it would be impossible to use fluorite in standard lenses. This challenge failed to quell the enthusiasm of Canon researchers, as they took up the task of developing fluorite into a viable optical material for use in high-performance lenses.

Differences in the convergence point of wavelengths of light affect the sharpness of an image transmitted through a lens, and appear in photographs as colour bleed. This is technically known as “chromatic aberration.” The key to designing a high-performance lens is to find configurations that correct chromatic aberration. Typically, a low-dispersion convex lens and a high-dispersion concave lens are used in combination to standardize the direction of light waves and align them all at a single convergence point.

However, careful examination of the area surrounding the convergence point of such a lens will reveal a residual aberration in the focal point for green wavelengths, which disperse between the red and blue. This slight residual chromatic aberration is known as secondary chromatic aberration or secondary spectrum aberration. Fluorite is characterized by extremely low dispersion, and unlike optical glass, its dispersion is exceptional. Therefore, it can play a significant role in eliminating this persistent secondary spectrum aberration. When a convex fluorite lens is used, to reduce chromatic aberration in the secondary spectrum, the red, green and blue focal points converge almost perfectly, at a single point. In 1968, two years after the launch of the F Program, Canon researchers successfully produced a synthetic fluorite crystal.

But numerous hurdles remained before fluorite could be used in a camera lens. Because fluorite cannot be ground in the same manner as optical glass due to its fragility, Canon drew upon its legacy of lens grinding technology to develop a special technique for handling fluorite. This grinding process takes four times longer than standard techniques, and afterwards, each lens needed to be washed by hand.

In 1969, Canon finally succeeded in producing a lens from fluorite — the FL-F300mm f/5.6 was the world’s first* camera lens to incorporate a fluorite element. Because longer focal length makes telephoto lenses more susceptible to the effects of secondary spectrum aberration, fluorite made a significant contribution to the performance of this lens. Today, the Canon L-series of fluorite-based super-telephoto lenses, characterized by refined delineation and exceptional high contrast, have earned a loyal following among photographers all over the world.

* Refers to lenses for general consumer-use, interchangeable-lens cameras.

UD lenses

Though fluorite offers superior optical characteristics, the high production cost makes it unsuitable for more widespread use. In order to extend ideal performance to an wider range of camera lenses, Canon set out to develop a new type of optical glass with characteristics similar to fluorite. In the early 1970s, Canon succeeded in developing Ultra-low Dispersion (UD) glass. Compared to standard optical glass, UD glass exhibits a lower refractive index, low dispersion and excellent partial dispersion characteristics. Therefore, an optimal combination of UD lenses can achieve nearly the same effect as fluorite. The development and realization of these high-performance fluorite and UD lens elements led to the creation of the "L-series" line of "Luxury" high-quality FD-mount lenses in 1978.

In 1993, Canon developed Super UD glass, a dramatic improvement over conventional UD glass. A single Super UD lens can do the job of two conventional UD lenses, essentially offering the same optical characteristics as fluorite. First used in the EF400mm f/5.6L USM lens, Super UD glass significantly reduces chromatic aberration, while also helping to reduce the size of the total lens to improve portability. The exceptional performance of Super UD glass makes it a central feature of many L-series lenses.

Aspherical lenses

Canon’s L-series lenses owe their high performance and crisp image resolution to an advance in optical technology that offers truly revolutionary optical characteristics — the aspherical lens. Aspherical lenses offer impressive sharpness and vivid detail that it almost seems like a veil has been lifted to reveal the visible world behind the lens. For years, aspherical lenses were only a dream for optical engineers, since their actual fabrication is so difficult. Aspherical lenses differ from conventional photo lenses — which are spherical — as a part of the spherical surface of the lens element has to be cut away at the optical axis. However, these lenses faced theoretical limitations due to their inability to converge parallel rays of light at the same focal point. The solution was to fabricate an aspherical lens with an ideal curvature, which converges parallel rays at a single focal point.

In some aspherical lens designs, the degree of asphericity is very slight. To the naked eye, it appears identical to a spherical lens. The degree of curvature is so slight that precision processing tolerances must be calculated to within 0.1 micron (1/10,000th of a millimeter). Though certain issues relating to mass production had not been completely resolved, at the time, Canon introduced the FD55mm f/l.2 AL in 1971. It was the world’s first SLR camera lens (without mirror-lock mechanism) to incorporate a ground aspherical lens element. The strong reception this lens received prompted Canon to increase production volume and accelerate aspherical lens research. Just two years later the company was able to introduce the world’s first nanometer-class mass-production equipment (with tolerances of less than one-millionth of a millimeter).

The lenses are polished precisely to a precision of just 0.02 micrometers, which is just 1/32 the height of a wavelength of visible light. This exacting precision ensures that the lenses will deliver high optical performance that one can only find with the L-Series.

Aspherical lens manufacturing technology continued to evolve. In the 1980s, research and development of large-diameter glass-molded (GMo) aspherical lenses began, and in 1985 these elements were successfully put to practical use. Glass molding technology uses high-temperature melted glass and aspherical, high-precision metal molds, to achieve superior surface tolerances. In 2007 the technology was used to make the first concave aspherical lens. The same technology has been used in many of today’s RF L-series lenses.

One Canon aspherical lens that satisfies a variety of needs is the replica aspherical lens, which was developed for the EF lens series in 1990 and is characterized by a high degree of design freedom in terms of the size, and the type of material used to make the spherical base lens element. In the RF lens series, the RF24-105mm F2.8 L IS USM Z also uses a replica aspherical lens. Improvements in the manufacturing process have given replica aspherical lenses a surface precision superior to that of EF lenses. In addition to offering greater freedom in optical design, the size of the new lens has been reduced while providing a focal length of 24mm-105mm with consistent performance at a bright aperture of f/2.8.

High-temperature melted glass and aspherical lenses

BR lens

By developing fluorite and UD lenses, Canon has been able to suppress the chromatic aberration that was typically found when using conventional lenses. Previous technology was not able to eliminate chromatic aberration and reduce the size and weight of the lens at the same time, particularly in the case of wide-aperture lenses with low F values. Chromatic aberration is caused by the dispersion characteristics of light. Ideally, all of the light passing through a lens should converge on a single point on the focal plane. Unfortunately, differences in the refractive index of different wavelengths inevitably cause some dispersion. This is the real cause of chromatic aberration (color bleeding). Wavelengths in the blue range of the spectrum are particularly difficult to correct, and cannot be fully resolved merely by combining concave and convex lenses. Inevitably, this creates some chromatic aberration.

To solve the problem, Canon developed the "BR Lens", a composite lens in which BR (Blue Spectrum Refractive Optics) optical elements with anomalous dispersion characteristics that greatly refract blue (short wavelength range) light are sandwiched between concave and convex glass lenses. BR lenses allow for greater freedom in lens design, because the other lens elements can be arranged in ways that may produce considerable chromatic aberration, but the blue wavelengths can then be largely corrected by the inclusion of the BR lens element. By developing new types of lens materials in this way, Canon is introducing lenses that can offer unique optical characteristics, while also improving performance and reducing size.

Floating system

Nowadays, optical technology has reached a level where it is possible to produce high-quality images at any shooting distance. Generally speaking, when you use an RF or EF lens, it is unlikely that you will notice any difference in the imaging performance regardless of the shooting distance. This is because the design of most lenses today includes elements that correct for various types of aberration, based on the range of shooting distances at which the lens is most often used. However, when the subject falls outside this “standard range” (particularly when the subject is closer than the distance for which the lens was designed), it is more likely that some sort of aberration will occur.

The degree of performance degradation will depend on the aperture setting, and the type of optical system being used. The shorter the focal length and the larger the aperture, the greater the potential for aberration. Wide-angle lenses, in particular, experience greater image curvature at short distances. If the center of the image is sharp, there will be some blurring at the periphery, while a sharp focus at the periphery will result in blurring at the center of the image. To solve this problem, Canon developed floating mechanism technology that provides ideal aberration correction at all shooting distances.

This minimizes aberration at all shooting distances, delivering excellent imaging performance from close range to infinity. This floating system is used in the EF24mm f/1.4L II USM and other large-aperture wide-angle lenses, as well as the EF180mm f/3.5L Macro USM, allowing them to achieve crisp imaging performance at close range. Large aperture lenses, even those with a near-symmetrical lens structure, tend to experience spherical aberration when used at close range. For this reason, a floating mechanism is used in EF lenses such as the EF50mm f/1.2L USM and EF85mm f/1.2L II USM, and also in RF lenses such as the RF70-200mm F2.8 L IS USM and RF100-500mm F4.5-7.1 L IS USM. Unlike the mechanism used in wide-angle lenses, the rearmost lens element of these lenses is fixed in place, while the floating mechanism allows the other elements to be movable. This helps to ensure excellent imaging performance and minimized lens flare at all shooting distances.

Super Spectra Coating

Canon has identified four factors that need to be met in order to make the ideal photographic lens:

• 1. Light rays from a single point on the subject should converge on a single point after passing through the lens;
• 2. Any flat surface perpendicular to the optical axis should be reproduced as a flat surface;
• 3. Any flat object perpendicular to the optical axis should be reproduced identically, without distortion;
• 4. colours of the subject must be reproduced accurately.

This final requirement is one that Canon itself singled out as a major development objective. In this quest, Canon established its own standard for uniform colour reproduction in the 1960s, when professional photographers first began using colour reversal film. Canon started with the assumption that any lens should deliver the same colour reproduction. But to evaluate colour precision, it is necessary to establish some criteria for colour reproduction and balance. Canon began by studying the characteristics of sunlight, and in particular the changes in light over the course of a year, as air quality and the angle of the sun varies. In addition to repeated test photos, Canon solicited feedback from numerous panelists. The data accumulated in this process was then converted into numeric values, to eventually establish Canon’s own colour reproduction standard for lenses. In the 1980s, when the photographic industry introduced the ISO colour Contribution Index as the industry standard, they adopted values virtually identical to those already being used by Canon, though Canon’s standards are a bit stricter, with less tolerance for variations.

Super Spectra Coating (SSC) technology was developed to help Canon meet this strict colour reproduction standard. This multi-layered coating creates a hard, durable lens surface with stable characteristics, and reduces the chances of lens flare and ghosting caused by reflections on the lens surface. When used on digital cameras, which are especially susceptible to lens flare and ghosting, Super Spectra Coating delivers optimal colour balance. Efforts to optimize coating performance continues, as Canon strives to respond to changing times and meet the changing requirements of professional image makers.

SWC: Subwavelength Structure Coating

Lens surface coatings are thinner than visible wavelengths of light. Canon uses an evaporating deposition method known as “evaporated film coating” to coat the lens surface with an ultra-thin layer that reduces reflection from the lens surface and boosts light penetration, in order to minimize lens flare and ghosting. However, the anti-reflective properties of evaporated film coatings tend to decrease as the incident angle of light entry and exit becomes sharper. Therefore, to improve imaging performance further, it is necessary to find even more effective ways to restrict light reflection. Since evaporated film coating had reached the limits of effectiveness, Canon had reached an impasse in the development of new optical arrays.

The technological breakthrough that took anti-reflective film coatings to the next level is known as Subwavelength Structure Coating (SWC). This technology makes it possible to control lens flare and ghosting even on lens surfaces that previously could not be suppressed with evaporated film coating. The anti-reflective principle underlying SWC is based on continuous variation of the refractive index. Reflections from the lens surface are caused by the differential between the refractive index of glass and that of air. By placing a layer of material with a continuously varying refractive index between the glass and the air, it is possible to smooth the transition of light from air to glass or from glass to air, thus minimizing reflection.

The solution was discovered in nature: The eyes of a fly are covered with minute (nanometer-scale*) convex-concave protuberances. This structure forms a layer with a very low refractive index, effectively preventing reflection. Canon technicians studied this principle in great detail, through extensive trial-and-error experiments, until they finally succeeded in developing a revolutionary coating technology that deposits a layer on the lens surface with nanometer-level structure. This consists of protrusions on the lens surface that are just 200-400nm in size, smaller than the visible wavelength of light (approx. 400-700nm). The layer is deposited evenly across the lens surface with the protrusions exposed to the air. This produces a gradual variation in the refractive index from the tip of the coating to its base, effectively absorbing incident light and guiding it through the lens surface. This revolutionary technology was first used in the EF24mm f/1.4L II USM lens, opening a new frontier in wide-angle lens performance.

*1nm=1 millionth of a millimeter

ASC: Air Sphere Coating

Air Sphere Coating (ASC) is a lens coating technology developed to enhance the anti-reflective properties of photographic lenses. Lens coating technologies developed by Canon include Super Spectra Coating (SSC) for reduced ghosting and flare and consistent colour balance, and the groundbreaking Subwavelength Structure Coating (SWC) which prevents light from entering the lens at high angles of incidence and significantly enhances anti-reflective qualities. Used in conjunction with SWC, the new ASC technology further reduces the chances of lens flare and ghosting.

Ghosting and lens flare are caused when secondary reflections between the lens elements and the image sensor cause light distortion or effects that degrade image quality. When shooting into the sun, or in other strongly backlit conditions, part of the image may be obscured by lens flare, which appears as an overexposed white patch. Reflections on the surface of the lens may also appear as clutter in the image (ghosting). ASC is Canon’s most recent step in the evolution of coating technology. It ensures that light always strikes the surface of the image sensor at an ideal angle, thus greatly reducing the chances of lens flare and ghosting.

ASC is a technology used to add a thin film made of silicon dioxide and air on top of the vapor-deposition lens coating to suppress the reflection of light. The coating contains a precise ratio of air, which has a far lower refractive index than optical glass, to give this layer an ultra-low refractive index. This gives it exceptionally strong anti-reflective properties, particularly for incidental light that enters at an angle almost perpendicular to the lens. When combined with SWC, which suppresses the secondary reflection of light entering at high angles of incidence, ASC ensures that any extraneous light entering the lens can be suppressed, regardless of the incoming angle, to effectively prevent lens flare and ghosting. Since ASC can be used on lens surfaces with various curvatures, it places fewer limitations on lens design.

Fluorine coating

For photographers who often work in adverse weather conditions, dirt or dust on the lens surface can directly affect the quality of their work. Fluorine coating, which is applied on top of the anti-reflective coating on the lens surface, makes it easy to remove any dirt from the lens. The coating is highly oil- and water-repellent, yet maintains optical transparency. Any smudge or oil on the lens surface can be easily removed by wiping with a dry cloth, with no need for lens cleaner or solvent. Static electricity caused by dry-wiping is also reduced, and the extremely smooth surface does not scratch easily.

Since dust or dirt on the lens surface can be quickly and easily removed, the photographer can spend less time worrying about keeping the lens perfectly clean, and instead concentrate more on shooting. Since most smudges can be removed with just a blower and a cloth, camera kits can be made more compact. This new coating technology delivers a multitude of benefits for the busy photographer.

Notes:

•If dirt and dust get onto the lens surface, always clean with a blower before directly wiping with a cloth.

•If the surface is wiped with lens cleaner or solvent, the high oil- and water-repellency may cause solvent to bead, preventing it from drying and making it difficult to wipe off.

DS coating

One key objective of Canon’s lens development efforts is to achieve superior optical performance when rendering out-of-focus areas of the image, as well as the parts that are in focus. This is particularly important when trying to take pictures with a bokeh (unfocused background) effect; the overall quality of the photo will depend on how effectively it depicts the out-of-focus areas. Bokeh is a photographic effect that conveys a very strong impression; it is one of the most important features of large-diameter lenses with wide apertures. In general, as the optical performance of a lens improves, the outlines of all portions of the image become clearer, even those that are out of focus. This result is not necessarily a positive one, in all situations. Sometimes, the sharper outlines can interfere with the bokeh effect in a way that makes the subject too emphatic. Canon realized that photographers prefer to have other options, in terms of how sharply each part of the image is rendered, when trying to create the bokeh effect.

Efforts to address this issue culminated in Canon’s proprietary Defocus Smoothing (DS) coating, a vapor-deposition film technology. The base lens design that adopted this coating was the RF85mm F1.2 L USM, an ideal portrait lens and a symbol of Canon’s optical technology. While maintaining its high resolution, high contrast, and suppression of chromatic aberration, this lens is capable of producing a unique bokeh effect that softens the outlines of a blurred subject. The coating gradually reduces light transmittance (light is blocked) from the center of the lens to the periphery, limiting the amount of light that passes through. The result is a lens that can produce bokeh images with soft, smooth contours.

For the RF85mm F1.2 L USM DS, a DS coating was applied to the surface of the foremost and rearmost lenses, in order to maximize the effect. The resolution of the in-focus areas of a subject is very high, while the contours are softly blurred. The lens can be used with a maximum aperture setting of F1.2, further enhancing the range of expression possible in portrait photography.

Provide users with bokeh expression options

With DS coating

Without DS coating

Smooth bokeh
with soft and
blurred outline

Bokeh with
sharp outline

Voice Coil Motor (VCM)

VCM unit

Looking ahead, the potential benefits of the RF mount are not limited to high image quality; it also offers the potential to enhance AF, operability, and mobility. Canon is pursuing advances in all of these areas. Actuators are no exception. Rather than simply rely on the drive systems that pioneered the RF lens era — such as Ring USM, STM, and Nano USM — Canon continues to pursue even higher levels of performance with technical advances that meet the needs of photographers. A good example of this progress is the newly developed Voice Coil Motor (VCM) actuator.

This new Canon technology converts electrical energy to kinetic energy using the power of magnets (a magnetic field). The coil is operated by moving the driving magnet back and forth, to shift the position of the magnetic field. This adjusts the position of the focal lens unit, which is attached to the coil linearly. Compared to conventional actuators, this technology enables swift and accurate, yet quiet movement of the focal lens group, even with lenses that are large and bulky.

The RF35mm F1.4 L VCM also provides electronic floating focus control by using VCM and Nano USM actuators in tandem. The VCM drives the heavier focus lens group while the lighter, floating lens group is driven by a compact Nano USM. By controlling the position of each lens group separately, the lens can achieve swift, smooth focus even with large-diameter lenses. The evolution of RF lenses continues unabated, making them the lens of choice for both still photos and movies.

In-lens drive systems

In 1985, as full-fledged autofocus technology was starting to hit the market, most manufacturers of autofocus SLR cameras adopted an in-body range-finding/body drive system, where the AF drive motor is built into the camera body, and the lens drive is operated by a mechanical coupler. Canon took a different approach, believing that the key to future market success was to abandon inhibiting technologies and construct a new system that could eventually surpass other systems in performance, responding to the photographer’s intentions immediately and accurately. This was the genesis of Canon’s new, high-precision AF system.

To optimize the efficiency of the overall imaging system, Canon abandoned the conventional in-body rangefinder/drive system, and instead decided to put individual motor drive systems inside each lens, and select an optimal motor design for each lens type, from fisheye to super telephoto. The Canon AF drive system is based on a design concept where "an optimal actuator for the lens, is placed as close as possible to the drive unit, and all information transmission and controls should be electronically controlled.” By locating the actuator next to the drive unit, Canon was able to boost efficiency, reduce energy transfer loss (and minimize noise) produced by the drive unit. Canon also expanded its range of actuators, designing units that can create the exact focus torque needed for each lens, so that even the largest lens is able to focus quickly and smoothly. In super telephoto lenses, where the drive unit is positioned far from the camera body, this system performs better than a body drive system, making it possible to create super-telephoto lenses with fast, and accurate autofocus. This is a key merit of the professional L-series lenses — the ability of the system to deliver high-performance, durability and operability in even the most severe conditions. This technology has been carried over to the EOS R system and RF Lenses, where technological innovation continues to improve its features and performance.

Large-diameter fully electronic lens mount

All imaging enthusiasts want their camera to function as if it is an extension of their body. In order to realize this wish, the EF lens adopted an innovative "fully electronic mount" that makes the operations between the body and the lens fully electronic eliminating the need for mechanical connections. When the mount is used, all data transferred between the EF lens and the EOS camera body is handled electronically. Autofocus communication links between the lens, and the body are maintained even when an extender is used, ensuring optimum operability and durability even in the most severe conditions. Canon’s large, 54mm diameter electronic lens mount provided the foundation for the design and production of the world’s brightest 35mm SLR camera lens — the EF50mm f/1.0L USM. This large-aperture lens can achieve fine detail and an attractive background blur (bokeh) even in candlelight, expanding the potential range of photographic expression. The large-diameter electronic lens mount design also facilitates the development of new lenses for the EOS R system, such as single-focal length lenses with large apertures and zoom lenses with higher magnification power.

Electronic lens mount (body side)Electronic lens mount (lens side)

RF mount

Canon introduced the EOS R System, and the RF mount, in 2018 — just over 30 years after the launch of the EF mount and EOS System. This imaging system marked the start of a new era for Canon, offering greater flexibility and growth potential. Since the objective of the EOS R System was to expand the range of possibilities to support the future needs of both photo and video users, Canon recognized the need for a lens mount with new specifications that would ensure maximum growth potential and optical design flexibility. Canon developed the RF mount as the foundation for the EOS R System, with its main focus to develop a new line of lenses to support an imaging system with the potential to evolve and advance well into the future.

The RF mount uses a large, 54mm-inner-diameter barrel and short back focus distance of 20mm to dramatically increase the optical design flexibility and support the development of new and unique lens designs. This mount has the potential to develop large-aperture standard zoom lenses with a maximum f-stop of f/2, such as the RF28-70mm F2 L USM lens — something that was not possible with earlier mount designs. Another major feature of the RF mount and EOS R System is the new 12-pin communication system. It greatly improves communication speed, instantly transmitting large volumes of data between the lens and the camera including information for: focus, zoom, aperture, image stabilization settings, lens aberration, and data for digital lens optimizers (DLO). These features allow the system to achieve outstanding image resolution, and a beautiful bokeh effect with a large, fully open aperture. The new control ring developed for the lenses also offers fine aberration correction and smooth operability. The RF series of lenses realizes new possibilities, continuing Canon's pioneering philosophy that the EF-mount series of lenses first pioneered.

Ring-type USM

By placing the drive motor inside the lens, Canon is able to fine-tune the motor design to match specific characteristics of the lens. Canon was the first camera manufacturer to successfully use an Ultrasonic Motor (USM) inside the lens to drive autofocus. The ring-type USM is powered by ultrasonic energy oscillations. Therefore, it is virtually silent, consumes little electricity, and is highly responsive to operational commands, making it ideal for controlling AF. First introduced in 1987 with the EF300mm f/2.8L lens, the quiet, high-speed autofocus performance of this USM was hailed as an astonishing achievement. Mass production technology for these motors was perfected in 1990. In subsequent years Canon continued to release sophisticated motors with enhanced performance, including compact, and mass-market models. Canon’s development efforts culminated in a full-time manual-focus system that integrates autofocusing and manual focusing capabilities — a revolutionary feature, particularly for professionals. After the AF has set an approximate focus, the camera operator can fine-tune the focus using the focus ring to achieve a specific, desired focus distance. This full-time MF feature is supported by many L-series and RF mount lenses.

Nano USM

The Nano Ultrasonic Motor (USM) is a compact ultrasonic motor that supports high-speed AF. It was first introduced in 2016, with the EF-S18-135mm f/3.5-5.6 IS USM lens. Using vibrational energy from ultrasonic waves, the motor moves in a straight line along a slider. The position of the focus lens, which is mounted on a rack-like component, can be adjusted along the optical axis with great precision, thus enabling high-speed AF. The very precise micro-movements of this revolutionary AF actuator helps the lens achieve high performance autofocus for both still photography and movie recording. In 2018, a new type of Nano USM was developed for the first time in an L-series lens. The new Nano USM has been miniaturized to fit within a compact lens barrel, to reduce the overall size of the lens as much as possible. It was first introduced on the RF24-105mm F4 L IS USM lens.

The new design of the Nano USM eliminates the spring that formerly applied pressure to a piezoelectric ceramic element on the back end. This structure has been replaced by springs positioned at the four corners of the unit, to significantly reduce thickness while maintaining high torque. The Nano USM is capable of driving a lens at high speed and stopping it with precision for high-speed AF when taking still photos. When shooting movies, it achieves smooth and near-silent focus for a wide range of expressive purposes.

STM

Canon first introduced the Stepping Motor (STM) in the EF40mm F2.8 STM lens. The STM has a smaller actuator than conventional ultrasonic motors (USM). This was a key factor in the development of Canon’s first pancake-type EF lens. The simple mechanical structure of the STM delivers high responsiveness and controllability when starting and stopping. There are two types of STM: a leadscrew type STM that offers exceptionally smooth AF drive, and a gear type STM that minimizes size. The gear-type STM was used in the EF40mm f/2.8 STM lens, and is currently used in a variety of RF-mount lenses. However, the RF10-20mm F4 L IS STM was the first L lens to adopt STM, and for good reason.

The USM has an advantage for lenses with long drive stroke, but the RF10-20mm F4 L IS STM was designed for a shorter stroke. Therefore, developers determined that an STM could be used, and still achieve good performance. The smaller actuator (compared to the USM) provides more freedom in designing the layout of the IS lens group. It is possible to place the image stabilizer (IS) mechanism on the sensor side, thus reducing peripheral blurring. Furthermore, the RF10-20mm F4 L IS STM is the first RF lens featuring an STM that comes with a position sensor. By shortening the start-up time, the overall performance of the lens is comparable to that of the USM.

gear-type

EMD

The Electromagnetic Diaphragm (EMD) is designed to work in tandem with the fully electronic lens mount system to provide high-precision digital aperture control. The EMD combines an aperture-blade unit and a deformable stepping motor. Compared to the system used in conventional cameras, where the aperture blades are opened and closed by mechanical levers in the camera, the new system is able to provide much higher precision control. The aperture can be controlled using an electronic dial on the EOS body, or using an electric pulse signal to set the calculated aperture value. Since no levers are involved, operation is smooth. The introduction of EMD also led to the creation of some very unique lenses, including the world’s first* TS-E lens with automatic diaphragm — an innovative and widely praised lens developed in 1991. In 2021, Canon developed the RF5.2mm F2.8 L DUAL FISHEYE lens, Canon’s first Stereoscopic 3D 180° VR lens equipped with two 5.2mm fisheye lenses. Both the right and left lenses feature separate, synchronized EMDs. Electronic signals can thus control the two EMDs simultaneously, to set the same exposure for both the left and right lenses for easy exposure adjustments.

* Refers to SLR cameras equipped with both tilt and shift functions (as of April 1991)

IS (in-lens image stabilization)

Whether one is an amateur photographer or a professional, the problem of camera shake — which results in blurry images — is often hard to avoid. The most conventional way to deal with camera shake is to increase the shutter speed (The minimum optimal speed is generally calculated as 1/x seconds, where x is the focal distance, measured in millimeters). To resolve this problem, Canon devised a high-precision in-lens image stabilization (IS) system that effectively compensates for camera shake. When an unsteady hand causes the camera lens to tilt as the shutter is pressed, light from the subject is bent relative to the optical axis. The result is a blurry photo. Canon’s in-lens image stabilizers work by shifting the position of the lens group, parallel to the focal plane. If the IS lens group shifts on a plane perpendicular to the optical axis to exactly match the degree of image shake, the light rays reaching the imaging surface will remain steady, resulting in a sharp, clear image. Canon uses two oscillation gyros in the lens to detect any degree of tilt, while a compact and highly responsive moving actuator adjusts the positioning of the IS lens group. The position of the IS lens group is then confirmed by sensors that provide feedback. The system places the optimal IS lens array in the optimal position for each lens. While the concept is simple, the result is exceptionally precise image stabilization. This adjustment also ensures that the image in the viewfinder remains steady, so it is easier to frame the subject and compose the photo.

This ability to accurately compose photos by looking through the viewfinder is one major advantage of in-lens image stabilization. Canon is committed to preserving its leadership in performance among manufacturers of high-performance, interchangeable-lens cameras. With many lenses available, from wide-angle to super telephoto, the broad lineup of Canon L-series IS lenses gives professional photographers a greater range of shooting options than ever before.

• 1. When lens is still

  

  To subject

  IS lens group

  Focal plane

• 2. When camera is shaken

  

  Camera shake

  Focal plane

• 3. Camera shake corrected

  

  Corrected light rays

  IS lens group shifts downward

Hybrid IS (in-lens image stabilization)

The goal of introducing image stabilization (IS) features in a macro lens has inspired camera designers since the initial development of IS systems. However, macro photography poses even greater challenges; in addition to conventional image stabilization, which compensates for a change in the lens angle, it is also necessary to compensate for positional shift: movements from side to side, or towards/away from the subject. This latter type of camera shake can noticeably affect the results, when shooting at close range. When taking photos of a distant subject, any movement that is parallel to the imaging plane has little effect on the results, but when taking macro photos, even a slight amount of movement can ruin an image. Canon set out to develop a system that would sense and compensate for both types of camera shake. The result was the Hybrid Image Stabilizer (Hybrid IS).

The technology to compensate simultaneously for both angle and shift camera shake was elusive: Canon’s solution was to employ two types of motion sensors and a new algorithm. In addition to the conventional angular velocity sensor, which was used to detect angle-based camera shake, the Hybrid IS system incorporates a linear acceleration sensor. Any camera movement detected by the two sensors is integrated using a newly developed algorithm, to calculate the degree and direction of the camera shake movement.

Hybrid IS is far more successful at capturing a stable image than conventional IS methods, even in the case of hand-held isometric (1x) photography, which has traditionally been very difficult. This allows the user to take high-precision handheld macro photos even when shooting in dimly lit venues where it is not possible to set up a tripod. The first lens to adopt this technology, the EF100mm f/2.8L Macro IS USM, gained widespread popularity and revolutionized the world of macro photography. The RF mount version RF100mm F2.8 L MACRO IS USM, which offers a maximum magnification of 1.4x, is also equipped with the Hybrid IS system. This further expands the possibilities for handheld macro imaging.

Coordinated Control IS

Canon has been developing and improving in-lens image stabilization (IS) systems for decades. IS functions have been incorporated in many EF and RF lenses, opening up new possibilities in imaging expression for photographers and videographers. The EOS R5 was the first EOS camera to feature an in-body image stabilization mechanism. The coordinated control of the in-lens IS, and the camera’s in-body IS achieves a camera-shake blur correction equivalent of an increase of up to 8.0 stops, in shutter speed. At the time it was released, this was the most effective IS* of any commercial camera. The IS mechanism works as follows: a gyro sensor/accelerometer is installed in both the camera and lens. These sensors, along with the camera’s live-view image, are utilized to detect motion or blurring with high precision, across the entire camera and lens. The camera shake data is then processed at high speed by the image processor and the lens CPU, to reduce detection errors between the camera and the lens. This calculates the appropriate correction ratio, and the camera and lens each make separate optimized corrections to reduce camera-shake blur. The impact that this has on image stabilization not only works for still photos, but for movies as well. This once again demonstrates the technological prowess that Canon has brought to the world of imaging.

* Refers to interchangeable-lens digital cameras available as of July 8, 2020 (both EOS R5 and EOS R6 have coordinated In-Body Image Stabilizer Still Shooting performance effective up to an 8.0-stop increase in shutter speed). According to Canon research.

Control ring

One feature that distinguishes RF lenses from previous Canon lens products is the control ring. The control ring is a feature available on many RF lenses, allowing the user to adjust various settings quickly utilizing their left hand, improving operability.

The RF mount of the EOS R camera body introduced a new 12-pin communication system that improves the coordinated operations between the lens and the camera body. This made it possible to assign various functions to the lens control ring. Aperture, shutter speed, ISO sensitivity, exposure compensation, as well as the AF method, white balance, and picture style can be assigned, selected and adjusted to suit the user's needs. In conjunction with the main dial and quick control dial on the side of the camera body, this new lens control ring offers unprecedented operability. For example, aperture control can be assigned to the lens control ring, while shutter speed and ISO sensitivity can be assigned to the main dial and quick control dial on the camera body. The user can then operate all three controls manually, using the left hand, right index finger, and right thumb, while looking through the viewfinder. The RF control ring is a perfect example of Canon's endless pursuit of the EOS concept of "speed, comfort, and high-quality imaging".

SA control ring

Since macro photography involves taking photos at a very close distance to the subject, background blur (bokeh) is achieved by adjusting the aperture, rather than adjusting the distance to the subject. Canon wanted to offer users greater creative freedom in achieving unique bokeh effects when taking macro photos. Canon recognized that the same principle could be applied to adjusting the spherical aberration (SA) as well, and this insight led to the development of the SA control ring. At the time, spherical aberration was generally viewed as a specialty lens feature that only served to decrease overall image quality. Canon overcame this stereotype by creating the means to control spherical aberration with high precision using a dedicated control, allowing users to achieve a softer or harder bokeh effect.

When Canon set out to design a RF Mount successor to the EF100mm F2.8L Macro IS USM lens — a favorite of many macro users — the optical design of the RF100mm F2.8 L MACRO IS USM allowed it to be the first Canon lens to adopt the SA control ring. This macro lens design, which offers a maximum magnification ratio of 1.4x, (exceeding the 1.0x magnification performance of the EF model), and also happens to be highly compatible with the SA control ring due to its floating lens system. This adds new functionality to adjust the character of the bokeh effect, to obtain soft focus, or bubble bokeh (hard bokeh) effects similar to that of older lenses, whether shooting at macro distances or at a normal distance. By rotating the SA control ring on the lens barrel, users can also adjust the softness of the subject in the in-focus area. This is useful when taking macro photos of subjects such as flowers, as well as portrait photos. The SA control and it's ability to adjust the bokeh effect provides new creative expression to macro and portrait users unlike any Canon lens before.

Ring: Rotate to the - side

Ring: Rotate to the + side

Past the focus position: Outlines of the bokeh become softer.
In front of the focus position: Outlines of the bokeh become harder.
At the focus position: Outlines become softer.

Past the focus position: Outlines of the bokeh become harder.
In front of the focus position: Outlines of the bokeh become softer.
At the focus position: Outlines become softer.

Inner and rear focusing systems

AF lenses use actuator motors to move the lens elements into proper position. Therefore, the weight of each lens element greatly affects the focusing speed. Canon has developed technologies for inner focus and rear focus designs that reduce weight by making only some of the lens components (those affecting focus) movable. This change facilitates precise and high-speed autofocus control. The design also makes it easier to downsize the entire optical system, contributing to a smaller overall chassis and improved weight balance for easy holding. Since the entire lens is an integrated unit, this also makes it more robust and durable. While most people tend to focus on the AF performance of the camera (body) itself, in reality the AF performance of the RF lens is an essential factor in determining the AF performance of the entire system.

RF24-105mm F4 L IS USM
(when focus distance is set to infinity)

Focus lens element:
Moves in the direction of the mount as the focus distance changes from minimum-distance to infinity

Full-time manual focus

Manual focus (MF) is often preferred for macro photography and other shooting situations that require precise focusing. However most photographers want to use autofocus (AF) to quickly get the subject into focus. The answer in such situations is the full-time manual focus (AF + MF) setting. After using One-shot AF to get an approximate focus, the final focal adjustment can be made manually by the user, by rotating the focus ring on the lens while still in AF mode. Full-time manual focus is extremely effective when you want to focus on a precise detail in macro photography, like one part of a flower. After a rough autofocus adjustment, the user can make adjustments to get the desired target in focus. This function was first introduced in the early EF lens series, and is now available in many RF lenses.

The ultimate in toughness and durability

Canon’s goal is for the camera user to have the ability to capture the moment instantly, effortlessly, and effectively, with confidence, even in the most difficult weather environments. The L-series lenses, in particular, were intended for professional use and designed to ensure stable, trouble-free performance even in the most severe working conditions. To ensure the highest overall reliability of each and every lens, Canon considers the user's working conditions at the start of the product design phase. Dust and rain are just some of the elements that a working professional must deal with when working outdoors, so they need a camera and lens that can function as a reliable precision instrument regardless of these conditions.

With Canon L-series lenses, the ring Ultrasonic Motor (USM) and other mechanisms perform to professional specifications regardless of the shooting environment. Every lens that bears the Canon name must deliver high reliability. To this end, Canon maintains rigorous production quality control standards at every phase, from designing the optical array to engineering mechanical parts. Production tolerances for lens element spacing, tilt, eccentricity and other specifications are measured to microns. When necessary, lenses are fine-tuned one by one to maintain this high level of quality. Today, the L-series sets the ultimate standard of Canon reliability, with performance that can satisfy even the most demanding professionals.

Weatherproof

Interchangeable lenses are precise optical instruments and indispensable tools for the working professional. These tools must perform to match or exceed expectations in rugged conditions. Rain or shine, indoors or out. Canon considers feedback from the professionals who actually use our lenses to be an important factor in the effort to boost lens performance. Professionals often have to work in severe conditions, subject to dust, wind, rain and snow. When Canon introduced a newly developed series of dust- and water-resistant super telephoto lenses in 1999, it assumed from the outset that its products would have to perform under severe conditions like these.

Today, the effort to meet these exacting standards continues. A rubber ring was introduced at the mount connection, to seal the gap between camera and lens from the elements when the two are attached. Highly dust and moisture-resistant construction was also used for the focus ring, focus preset playback, and other moving parts. Switch panels and drop-in filter holders were rubberized. In today's age of digital imaging, the performance of professional lenses will be tested in an ever-growing range of environmental conditions, just as professionals demand they deliver superior imaging performance. Canon’s pursuit of excellent dust and water resistance continues in the RF L-series lenses. The entire system including lens, body, and accessories are designed to satisfy the most exacting demands of professional image makers.

* This cannot guarantee complete exclusion of water and dust from entry. The lens must be attached to the camera body to ensure dust- and moisture-resistant performance.

White lenses

L-series telephoto and super telephoto lenses are easily identified by their white lens barrels. White is an appropriate colour for professional lenses, which often must operate in the heat of a blazing summer sun. In 1976, the FD600mm f/4.5 S.S.C. and the FD800mm f/5.6 S.S.C. were the first SLR camera lenses to feature a white surface, to prevent heat from accumulating in the lens barrel. In subsequent years, the “white barrel” lens has become a symbol of the professional quality of Canon lenses, and is recognized by photographers and videographers everywhere. In the era of EF lenses, the reputation of the white-barrel lens has only grown with each new improvement to performance.

White-barrel lenses are admired for their outstanding expressiveness, and for a high-speed AF that can capture even the fastest of subjects like the thrill of motor sports. At any world-class sporting event, the predominance of white barrel lenses in the press pack can attest to the ability of the L-series lenses to capture every dynamic moment. Imaging is an ever-changing form of expression, and advances in digital technology have raised expectations of lens performance to new levels. The letter ‘L’ represents a benchmark in imaging performance. It denotes a top-quality professional tool that can meet the professionals highest demands and support their work at the cutting edge of their profession. But even this benchmark is just another point along the way. At Canon, the pursuit of the ideal lens quality never ends.

Heat shield coating

Canon’s efforts to address heat accumulation with our traditional white-barrel lenses have reached a new stage. To ensure that its lenses maintain outstanding optical performance when used in hot, direct sunlight, Canon adopted a heat-reflecting white coating for the barrel of some lenses, rather than the more traditional black. The history of white-barrel lenses stretches back to the FD600mm f/4.5 S.S.C and FD800mm f/5.6 S.S.C., two large-aperture telephoto lenses released in 1976 for single-lens reflex (SLR) cameras.* Canon’s in-house efforts to develop heat shield coatings originated as a way to make lenses more reliable under high temperature conditions. Through trial-and-error research into the selection and composition ratio of coatings, Canon identified ways to enhance reflectivity toward light in the infrared spectrum, and developed new technologies to suppress temperature increases in both the coating film and the coated items. The final result is a series of white-barrel lenses that offer greater reliability when shooting in the hot sun.

• 

  Traditional white coating

• 

  Heat shield coating

Our heat shield coating uses infrared-reflecting pigments to enhance reflectivity against the “heat” component of sunlight. In the past, Canon lenses have offered either a carbon black or a white titanium oxide surface coating. However, carbon black strongly absorbs infrared waves, offsetting some of the reflectivity improvements offered by the heat shield coating. Our newly developed heat shield coating enhances reflectivity by replacing carbon black with an infrared-reflecting pigment. The coating also uses titanium oxide with a silica covering, making it more resistant to UV weathering. It is highly resistant to damage caused by scratching or abrasion. Lenses with the new coating retain Canon’s signature “white-barrel” color. Heralding in a new age for white-barrel lenses, the Canon heat shield coating was first introduced in the EF400mm f/2.8L IS III USM and EF600mm f/4L IS III USM, and is now used in all RF lenses with a white body.

* For single lens reflex cameras lenses. Also used in the TV2000mm f/11 super telephoto lens for broadcast cameras, launched in 1960.