What is a lens?
Superficially, a lens is little more than a cylinder containing optical elements that shift about as you focus by turning a ring around the cylinder. But even in its most basic form, a camera lens is far more complex than it might appear.
A lens is more than the sum of its parts. When you attach a lens to a camera, your choice of lens is very much like a painter's choice of brush. For finer details, the painter will choose a narrow, pointier brush. For cloud-free skies, a broader brush would be a wiser choice. Wide-angle lenses are typically best used for wide-field landscapes and tight interior photos, while telephotos are best for bringing distant subjects closer and for portraiture, though one should never take these "rules" as absolutes.
Most photographers would avoid shooting a portrait with a wide-angle lens, but in the right surroundings and with careful placement of the subject in the frame, wide-angle lenses can be used to capture dynamic environmental portraits. Similarly, the compressive nature of telephoto lenses can add an equal measure of visual dynamics when shooting landscapes from a greater distance.
The criteria that determine the image quality of a lens include the number of elements the lens contains, the shapes of these elements, how they are grouped, the type of material they’re made of, and how they are coated. And then there's the lens's diaphragm and how wide it opens, the shape and number of the diaphragm blades, the lens mount, the autofocus motors, the image stabilization system (if any), and so on.
The evolution of lens design, from singles to fluorite
There are five basic types of camera lenses, the most basic being a "single," which as the name implies, consists of a single glass lens element. Singles are followed by "doublets," which are made up of two co-joined elements, followed by "double types," which contain two unattached lens elements, and "triplets," which contain three individual elements in a convex/concave/convex sequence.
Last are "symmetrical" lenses—a lens design containing two groups of one or more lens elements positioned on opposite sides of the lens diaphragm. Some of the more common symmetrical lens designs include Double-Gauss, Tessar, Planar, and Orthometer. Interestingly, the DNA of most modern lens designs can be traced back to the original Canon 50mm/ f1.8, a Gauss-type lens design introduced in 1951.
Today, Canon offers a gapless selection of more than 70 EF-series fixed focal length and zoom lenses designed to meet the challenge of almost any photographic scenario you could imagine.
What makes a lens a Canon lens?
If you were to ask Canon’s optical engineers to list the most important attributes and principles that determine high-quality lens design, they’d tell you the following:
- Light rays entering the lens from a single subject point ultimately converge at a single point after passing through the lens.
- Flat surfaces perpendicular to the optical axis reproduce equally flat in the final photograph.
- Flat objects perpendicular to the optical axis reproduce similarly and without distortion.
- Color values must be reproduced faithfully.
In a nutshell, their goals are to design lenses capable of capturing pictures that display edge-to-edge sharpness with accurately rendered color and contrast, and minimal distortion. To achieve these goals, Canon incorporates a combination of advanced optical, micro-electronic, and precision-manufacturing technologies to produce what is acknowledged to be an industry standard for image quality, lens design, and manufacturing quality.
Optical glass, fluorite, UD glass, and super UD glass
Optical glass is the basic ingredient of a camera lens. Qualifiers for optical glass include precise refraction and dispersion characteristics with equally strict standards for levels of transparency, color fidelity, warps, striation, and bubbles.
The standard with which optical glass is classified is called the Abbe number, determined by the composition and specific optical characteristics of the glass. There are about 250 distinct Abbe classifications, and it’s not unusual to find more than one type of Abbe glass in a single lens design.
Going beyond optical glass
In the process of designing the first-generation L-series lenses—Canon’s premium line of camera lenses—Canon’s engineers needed to go beyond the practical limitations of even the finest optical glass. After extensive testing in the lab and in the field, Canon began to incorporate elements made of Fluorite, a rare-earth material.
A notable quality of Fluorite glass is its ability to converge red, green, and blue light into points far narrower than conventional optical glass can, which greatly eliminates color fringing (chromatic aberration). Due to its inherently high level of optical clarity, Fluorite also produces higher measures of image delineation compared to conventional optical glass formulas.
The downsides of Fluorite glass include its rarity and the difficulty and expense of processing it and grinding it to high optical standards. In order to reduce the cost factor, Canon’s optical engineers developed cost-effective synthetic Fluorite crystals that could maintain equal measures of chromatic aberration control and faithful color characteristics, traits that made natural Fluorite desirable in the first place.
Fluorite elements led to the development of UD (Ultra Low Dispersion), glass, which exhibits low refractive and dispersion indexes and improved contrast and resolving power, followed by Super-UD glass, which is a further improvement in UD glass technology. As with Fluorite, the inclusion of UD and Super-UD glass technologies has enabled Canon's engineers to design lenses that are smaller, lighter, and sharper than their predecessors.
It should be noted that Canon has made a concerted effort to eliminate the use of leaded glass in its lenses. Despite the fact that lead is a naturally occurring element common to glass that’s environmentally safe when embedded in glass, Canon's optical engineers developed earth-friendly manufacturing processes that maintain the optical properties necessary to produce first-class camera lenses while remaining environmentally friendly.
What’s a "II" lens?
Many newer Canon EF-series lenses have a "II" included in their designation. These lenses are optically identical to their non-II predecessors, but have improved weather-resistant construction and improved anti-reflective barrel surfaces.
Canon "L" lenses
Canon’s top-of-the-line lenses are the "L" series lenses. Easily recognizable by the bold red line that rings the front of the lens barrel, Canon’s L-series lenses reign supreme in both image quality and construction detail. Though the letter "L" was originally intended to suggest the word "Luxury," the truth of the matter is that Canon L-series lenses are recognized among professionals and knowledgeable enthusiasts as being among the sharpest and best-built lenses on the market today.
Along with state-of-the-art Ultra Low Dispersion (UD) and Fluorite glass technologies, Aspherical lens surfaces, and Super Spectra Multi Coatings, Canon L-series lenses also feature tough alloy construction and are thoroughly sealed against moisture and dust.
Canon’s L-series lenses, specifically many of the telephoto zooms and prime telephotos, are recognizable by their distinctive white barrels. Actually more of a light gray or putty color, this lighter-color enamel is not applied for cosmetic reasons. Applying lighter-colored enamel to the external surfaces of the lens barrel helps minimize heat buildup, reducing the possibility of compromising sharpness levels of the lens due to glass expansion.
Canon was one of the first companies to apply lighter colors to the barrels of its lenses. As a result, when viewing the sidelines at sporting events, it was hard to ignore the fact that a majority of the pros photographing these events were shooting with this distinctively colored Canon gear.
On many black-barreled telephoto lenses, the focusing action travels beyond the infinity mark. This is a focusing compensation feature known as "over-focusing," and is used to compensate for heat expansion, which shifts the infinity mark when using dark-colored lenses in hotter, sunnier climates.
Aspheric lens surfaces
In a perfect world, all camera lenses produce images that are sharp (even at the edges), free of distortion, display zero optical aberrations, and reproduce color in true fidelity. The problem is that we don't live in a perfect world, which means if we want "perfect" lenses in a wide range of focal lengths and maximum apertures, we have to go beyond the basics.
In the case of faster, wider-aperture, and wider-angle lenses, optical aberrations and edge sharpness can be challenging, even among lenses made of the finest optical glass. To remedy the problem, Canon's optical engineers—with the help of advanced CAD computer applications—began adding free-curved or aspheric surfaces to their lens designs.
Unlike conventional convex and concave lens surfaces, aspheric surfaces feature additional dips and rises along the surfaces of the lens element that improve edge-to-edge image sharpness with a noticeable reduction of spherical aberrations.
Just as the small winglets at the tips of many commercial aircraft wings improve fuel economy by reducing drag as the wings slice through the air, aspheric lens surfaces improve overall image quality by maintaining high levels of resolving power equally and evenly across the entire image field.
Though more complex and expensive to design and manufacture, a single aspheric element can often replace two or more spherical elements, which in turn makes it possible to design lenses that not only perform better, but are smaller, lighter, and are often less costly to produce than traditional lens designs.
In addition to the ground and polished aspheric elements used in many of Canon's professional L series lenses, Canon also produces molded glass aspheric lens elements that are less production-intensive, along with precision-molded plastic lens elements consisting of ultraviolet-light-hardened resin surfaces that have aspheric surfaces molded into them for use in less expensive interchangeable lenses and advanced point-and-shoot cameras.
Diffractive optics (DO)
Canon currently produces two lenses that contain diffractive optics: the EF 400mm/f/4 DO IS USM and EF 70-300mm/f4.5-5.6 DO IS USM. Diffractive optics are made up of two or three glass elements, each of which has been coated on both sides with diffractive coatings, and bonded together into a single, multilayer DO element.
The advantage of DO elements is that they make it possible to manufacture smaller and lighter high-performance zoom lenses, allowing size- and weight-conscious photographers the ability to expand their optical range while maintaining the current size and weight of their camera bags. Frequent fliers take note!
Floating elements: maintaining edge sharpness on wide-angle lenses
When focusing at closer distances, many lenses begin to suffer from optical aberrations and loss of resolving power due to the extended distances between the lens groups.
To counter this phenomenon, Canon employs floating lens elements (aka close-distance aberration compensation mechanisms) that move independently from the main lens groups for the sole purpose of maintaining sharp, even detail across the image field and low measures of color aberration as the lens reaches its closest focusing point.
Though most commonly used in wide-angle lenses, floating elements can also be found in select Canon wide-aperture, mid-range telephoto, and EF-series macro lenses.
Lens coatings
Even the best optical glass formulations cannot narrow the entirety of the visible color spectrum to a single point of focus, nor can uncoated optical glass control flare and color aberrations due to stray light striking the lens surface. To improve upon the limitations of optical glass, coatings typically consisting of magnesium fluoride or silicon monoxide are applied thinly and evenly across both surfaces of each lens element.
Because light comprises numerous wavelengths, up to 10 layers of coatings (multi-coating) might be used as a means of maintaining evenly consistent color rendition throughout the visible color spectrum, with minimal degrees of flare and color aberrations.
Though logic would indicate otherwise, applying coatings to a lens element does not inhibit the light-transmitting qualities of a lens. In practice, lens coatings increase the light-transmitting qualities of glass by eliminating the inherent reflective characteristics of glass.
Canon lenses are coated with Super Spectra Coatings that help maintain sharp image detail, richly saturated color, and correct levels of image contrast even in backlit situations. Super Spectra multi-layered coatings, which allow up to 99.9% of full-spectrum light to pass through the lens, also provide for an additional layer of protective coating across the surfaces of each lens element.
A relatively new form of lens coating is Sub Wavelength Structure Coating (SWC), which is used on many L-series lenses to further minimize ghosting and flare when applied to the large-curvature lens elements found on many ultra-wide and long-telephoto lenses.
SWC coatings utilize microscopically thin layers of aluminum oxide narrower than the wavelength of visible light (220 nm) that limit the degree of reflective light to about 0.05%.
Along with Super Spectra and SWC lens coatings, smudge- and fingerprint-resistant Fluorine coatings are used on the surfaces of lens elements on select Canon EF-series lenses.
The mechanics of Canon lenses
EF, EF-S, and EF-M electronic lens mounts
There are three distinct families of Canon lenses. They include the EF mount, for use with Canon's full-frame (24 x 36mm) and APS-C (22.3 x 14.9mm) format DSLRs, the EF-S mount for use exclusively with Canon's APS-C format DSLRs, and the EF-M mount, designed for use exclusively with Canon EOS M mirrorless cameras.
What these lens mounts have in common are solid-state electronic components that enable near-instant communication between the camera and the lens. By replacing mechanical parts with electronic data-transfer control, Canon lenses are capable of achieving higher-speed autofocus and precision aperture control, which promises sharper, consistently accurate exposures under the most demanding shooting conditions.
Because the image circles on Canon EF lenses are designed to cover full-frame sensors, they can also be used on APS-C DSLRs, which have smaller (1.6x crop factor) surface areas. The opposite—mounting EF-S lenses on full-frame EF mounts—is not possible because the image circles of EF-S lenses are smaller than the circle size needed to cover a full-frame sensor. EF-S lenses are strictly for use on the EF-S lens mounts found on Canon APS-C format DSLRs.
Canon’s latest EF-M mount is designed for use with Canon’s APS-C format EOS M-series mirrorless cameras. Canon’s EF-M-mount focal flange distance is shorter than the standard EF mount (18mm versus 44mm) and the size and weight of EF-M lenses are correspondingly smaller and lighter.
Though EF-S and EF-M lenses are both designed to cover the same APS-C format image field, they are entirely different in design and cannot be used interchangeably.
A majority of Canon lens mounts are made of stainless steel. Select Canon lenses, including some of Canon’s lighter-weight, variable-aperture kit zooms and the 50mm f/1.8 II, are made of plastic. Though not as rugged as stainless steel, the plastic polymers used to manufacture these mounts wear well and are more than sufficient for use with these select, lighter-weight optics.
Electromagnetic diaphragms
A component found in every Canon EF and EF-S lens is an electromagnetic diaphragm (EMD). Unlike mechanical lens diaphragms, which do not always form consistently accurate aperture openings from one exposure to the next, EMDs form repeatedly accurate aperture openings each time they close down. And because they are electromagnetically controlled, lag time between the moment you press the shutter and the diaphragm blades close down is near nil. EMDs are also quieter and smaller than mechanical diaphragm assemblies.
Ultrasonic motors (USM)
A big challenge facing lens manufacturers is designing autofocusing systems capable of keeping the subject in sharp focus, regardless of the distance between 
the subject and the lens, and the speed of the subject as they pass through or across the image field.
To meet this challenge, many Canon lenses contain Ultrasonic Motors (USM) that unlike commonly used electromagnetic autofocus motors, utilize piezoelectric ceramic elements to produce rotational force, resulting in faster, quieter, and more accurate autofocus response times.
Focus preset
When shooting fast-moving action with longer focal length lenses, it can be difficult to shift focus fast enough to capture all the action. To address this problem, select Canon telephoto lenses feature a focus-preset control that enables you to pre-focus the lens at a set distance from the camera position. Once engaged, a twist of a ring instantly refocuses the lens to the preset focus mark faster and more accurately than trying to quickly shift focus manually, especially when shooting fast-action sequences.
Full-time manual focusing
Full-time manual focus override is another benefit of shooting with Canon EF lenses. As accurate as Canon AF systems are, there are times you want to tweak the focus for one reason or another. With most Canon lenses, changing focus on the fly is simply a matter of rotating the manual focus ring.
Focus Lock
A very handy feature found on many of Canon's longer telephoto and zoom lenses are Focus Lock buttons. Located along the circumference of the forward portion of the lens, Focus Lock buttons are essentially cut-off switches to the AF motors when shooting in Continuous AF mode, and they come in handy when you want to lock the focus at a specific point in the image area.
Internal and rear focusing systems
The focusing systems used in photographic lenses fall into three general categories: all-group focusing lenses, front-group focusing, and rear and internal focusing systems. The shortcomings of all-group and front-group focusing systems is that they awkwardly jut outward when focusing close to the subject, and have thread mounts that rotate as you focus or zoom, making it difficult to use polarizing or graduated neutral density filters.
To correct these issues, Canon EF lenses feature internal and rear focusing systems that do away with telescoping lens barrels and rotating filter threads. Inner and rear-focusing lens designs are also smaller, lighter, and have quicker autofocus response times, making them far more practical and easy to use.
STM (Stepping Motor Drive)
Stepping motor drives (STM) are one of the newer video-friendly Canon technologies. The key benefit of STM technology is its ability to focus the lens silently when shooting video with sound. Stepping motor drives are currently designed into all Canon EF-M lenses and select EF-S lenses.
Things to consider when purchasing your next lens
The difference between purchasing a new camera and purchasing a new lens is that you are most likely going to replace the camera you buy today at least once, maybe two or three times before you replace the lens you buy today. Unlike cameras that typically get facelifts, if not a complete revamping on a yearly basis, a popular lens design might stay in production for a decade or more. For this reason, it's worth the time and effort involved to research your options when choosing camera lenses.
Focal lengths and angles of view
There are three main categories of lenses: normal, wide-angle, and telephoto, and to make things interesting, because Canon manufactures cameras containing full-frame and smaller APS-C format imaging sensors, you can't always categorize a lens based on its focal length.
For example, when used on a full-frame (24 x 36mm imaging sensor) DSLR, a 50mm lens is considered a standard or "normal" lens. Mount the same 50mm lens on a compact camera containing a smaller, (22.3 x 14.9mm) APS-C sensor, and the image in the viewfinder now appears as if it was captured with an 80mm lens.
The lens is still a 50mm lens, but because the recording area of the APC-C imaging sensor is 40% smaller than a full-frame sensor, the recorded field of view (FOV) becomes correspondingly narrower (46.8° down to 30.3°), cropping the image field similarly to that of a narrower-angled 80mm lens.
For this reason, a wide-angle lens on a full-frame camera effectively becomes a semi-wide or normal lens when mounted on a camera containing a smaller imaging sensor.
"Equivalent" doesn't necessarily mean "the same"
A common misconception about crop factors is that when you say a lens has "an equivalent focal length," the term "equivalent" means the lens changes focal length. The cropped field of view might be equivalent, but the imaging characteristics of the lens remain unchanged.
As an example, a 60mm macro lens designed for use on an APS-C format camera is often described as being a terrific macro and portrait lens when, in fact, it's a terrific macro lens and a so-so portrait lens.
The problem is that, while a 60mm lens captures the field of view of a 96mm lens when mounted on an APS-C-format camera, it doesn't produce the same degree of portrait-friendly compression as an 85mm or 100mm short-telephoto portrait lens. It frames your subject similarly, but it retains the compressive characteristics of a 60mm lens.
The only way you can retain the face-friendly attributes of an 85 to 100mm portrait lens on a Canon APS-C format DSLR is to use an 85 to 100mm portrait lens and step back about 40% further from your subject in order to fill the frame to head-and-shoulder proportions.
When shopping for your next lens, keep this information in mind. By doing so, you’ll be less likely to choose the wrong focal length for your needs.
Lens choices
Fixed focal length or zoom lenses?
Camera lenses are available in fixed focal lengths and zoom configurations, both of which have plus sides and minus sides. The plus/minus issue can be best illustrated by Canon's EF-28-300mm /f3.5-5.6L IS USM, a sharp, L-series zoom lens that covers a full-frame camera from wide-angle through long telephoto. It's a true one-lens solution. And while its size is fairly manageable (3.6 x 7.2"), it weighs about 3.7 lb, which can take its toll on one's shoulders after a few hours of hiking around town or off in the woods. As they say, everything has its price.
The plus side of fixed focal length lenses is that, in most focal lengths, they are available with wider (faster) maximum apertures than zoom lenses. Fixed focal length lenses often focus closer, and in some (but not all) cases, are sharper than their zoom counterparts.
The down side of fixed focal length lenses is that they are not as versatile when shooting subjects that move quickly toward or away from your camera position. The only way to zoom when shooting sporting events or wildlife with fixed focal length lenses is to physically change camera position, which is not always possible or practical.
Zooms offer far more flexibility when shooting sports, wildlife, and similar fast-action subjects simply because they allow you to reframe your subject quickly and easily without having to change your shooting position, which is a priceless commodity when shooting from a fixed vantage point.
When shooting with zoom lenses, it's easy to get lazy. When shooting with a fixed focal length lens, you have to physically approach your subject in order to frame the picture properly. With a zoom lens you see something and you zoom in on it. And while there's nothing wrong about shooting that way, one of the benefits of a zoom lens is that it makes it extremely easy to photograph a subject from a variety of vantage points, distances, and focal lengths without having to pause and switch lenses.
If you are shooting with a 16-35mm wide zoom, the differences between filling the frame with your subject at the 16mm end of the focal range will create imagery far different than pictures captured at 35mm from a greater distance. The same can be said for 24-70mm zooms and 70-200mm zooms. Whenever time allows, always explore your subject at different focal lengths and distances.
If there were a downside to shooting with zoom lenses, it would have to be that none of them opens up wider than f/2.8, and if they did, they would be quite hefty. It's not that zoom lenses with wider maximum apertures (i.e. f/2 or f/1.4) would be impossible to design and manufacture, but you’d have to mount them on a forklift if you wanted to shoot with one. Reading the spec sheets of a 70-200mm f/1.4 or 16-35mm f/1.4 zoom would be amusing, to say the least.
Are fixed focal length lenses are sharper than zooms? It would be fair to say many modern zooms rival their fixed focal length counterparts in terms of resolving power, contrast, and overall image quality. And they're all capable of taking really good photographs.
Constant and variable-aperture zoom lenses
Zoom lenses come in two varieties: constant aperture and variable aperture. Constant-aperture lenses, which maintain a consistent maximum aperture regardless of the focal range, tend to be faster (i.e. have wider maximum apertures) than most variable-aperture models. Constant-aperture zooms also tend to be larger, heavier, and often pricier compared to their variable-aperture counterparts.
Variable-aperture zooms lose their ability to transmit a constant volume of light as the lens zooms from wide-angle to telephoto, which is why a zoom might start off at f/3.5 at the wide-angle position, but max out at f/5.6 or f/6.3 at the telephoto end of the focal range. As you zoom in, less light finds its way to the imaging sensor.
It’s important to keep in mind that while variable apertures are synonymous with kit zooms, variable apertures can also be found in a few of Canon’s top-tier L-series lenses. In other words, never judge a lens by its f/stops.
Image Stabilization
Depending on the lighting, the focal length, and the maximum aperture of a lens, there comes a point at which it becomes increasingly difficult to capture sharp pictures due to camera shake. As a rule, it’s not advisable to handhold a camera at a shutter speed slower than the numerical value of the focal length of the lens being used on a full-frame 35mm camera (1/focal length-second).
In other words, if you are using a 50mm lens on a full-frame camera, do not handhold the camera at speeds slower than 1/50-second. In the case of a 200mm lens, keep the shutter speed above 1/200-second. When shooting with a 20mm lens, you can comfortably drop the shutter speed down to 1/20-second. This isn’t to say it’s impossible to handhold a 500mm lens at 1/125-second and get a sharp picture, but chances are your results will be far better at 1/500-second.
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To ensure sharp pictures at lower-than-recommended shutter speeds, image stabilization (IS) is incorporated into certain lenses in order to minimize the appearance of camera shake and enable greater handholding capabilities.
Canon’s latest-generation IS system relies on twin oscillating gyroscopes that detect shake-related disturbances' path (or as optical engineers call them, "angular velocity disturbances") to the image and corrects them by shifting an independent image-stabilizing lens group on a plane opposite to the direction of the lens movement, which cancels out the movement, maintaining an unbroken path for the incoming light rays.
So instead of having to maintain shutter speeds no slower than 1/400-second, a photographer using a Canon EF 400mm f/4 DO IS USM lens can now capture sharp image files at shutter speeds as low as 1/25-second.
In addition to standard IS mode, select Canon IS-enabled lenses feature an IS Mode 2, which allows for image-stabilized panning shots of moving subjects. When switched to IS Mode 2, the IS system is designed to detect panning movement and automatically switches off the IS sensors that monitor horizontal motion. This allows the stabilization system to focus on vertical movement.
An image-stabilization feature found exclusively on Canon’s EF-M lenses is Dynamic IS, which in addition to smoother low-light imaging, features a stepping motor for quieter and smoother video operation.
It should be noted that all Canon IS-enabled lenses are tripod and monopod compatible. Unlike other manufacturers' image-stabilization systems, which should be turned off when using a tripod or monopod, Canon IS lenses are designed to detect these support devices and automatically disengage the IS system.
The advantages of wider (faster) lens apertures
When shopping for a lens, it's not unusual to find a choice of lenses that, while equal in focal length, feature varying maximum apertures. As an example, Canon offers 50mm lenses with maximum apertures of f/1.8, f/1.4, and f/1.2. Each of these lenses is an excellent optic and is capable of taking fine photographs, though they differ in low-light capture abilities, weight, size, close-focusing range, and price.
For casual snapshooters, the slower, least expensive Canon EF 50mm f/1.8 II is sufficient for almost every need. For others, the EF 50mm f/1.4 USM, which is a third of a stop faster and features a sturdier stainless-steel lens mount, may be preferable. For pros and others who require even better low-light shooting capabilities, Canon's legendary EF 50mm f/1.2L USM is the lens of choice.
Low-light shooting capabilities aside, other reasons many photographers choose faster lenses is because wider aperture lenses also make it easier to isolate the subject from the background and foreground (selective focus), which draws the viewer’s attention directly to the subject. This is why portrait and fashion photographers prefer wider-aperture lenses.
Combined with the faster top-end shutter speeds (1/4000 - 1/8000th-second) afforded by modern DSLRs, these also make it possible to shoot wide open under bright midday skies without having to resort to neutral density filters. Wider-aperture lenses also make it possible to maintain faster shutter speeds (and brighter viewfinders) when using polarizing filters.
Selective focus and maximum apertures
The maximum aperture of a lens plays a big part in determining the characteristics of the final image. As an example, two lenses of similar focal lengths, one with a maximum aperture of f/2.8 and another with a maximum aperture of f/1.2, when used at their widest apertures, will produce images that are quite dissimilar in terms of how much of the subject is in focus and not in focus.
This is one of the reasons fashion, beauty, portrait photographers, and journalists often opt for an f/1.2 or f/1.4 version of a lens, even though they can purchase a very able f/1.8 or f/2 version of the lens for a third to half of the price of the faster model.
The slower, less-expensive models take excellent pictures, but pictures taken with the wider-aperture lenses have a totally different visual character because of the unearthly interplay between sharpness and blurriness that only happens when shooting wide open with an f/1.2 or f/1.4 lens.
Circular-aperture diaphragms and "bokeh"
When discussing image quality, the terms "natural-looking" or "pleasing bokeh" are often used to describe the quality of out-of-focus highlights in a photographic image.
The term "bokeh" is often mistakenly used to describe selective focus, which itself describes a method of isolating the subject, or a portion of the subject, by shooting at the lens’s widest maximum aperture, causing the foregrounds and backgrounds to go blurry.
Bokeh is a transliteration of the Japanese word "boke," which according to most accounts, describes the aesthetic qualities of the out-of-focus portions of a photograph, specifically, whether or not the blurriness is aesthetically pleasing to eye.
Pleasing or good bokeh describes out-of-focus highlight areas that appear circular or gently swirling, rather than polygonal, geometric, or linear. Do keep in mind, although generally agreed upon, good or bad bokeh is subjective and ultimately a matter of personal taste. Traditionally, the aperture diaphragms used in camera lenses consist of straight-edged blades, which cause out-of-focus highlight areas within a photograph to appear polygonal, which is not the way the circular pupils of our eyes interpret these areas. Canon’s optical engineers resolved this problem by incorporating diaphragm blades with curved edges that emulate light patterns closer to the way our eyes interpret the world. As a result, Canons EF-series lenses are often praised for their pleasingly natural bokeh.
Choosing your next lens
Wide-angle, ultra-wide-angle, and fisheye lenses
Wide-angle lenses can be broken down into two distinct categories: rectilinear and fisheye. Unlike fisheye lenses, which capture images that display curvilinear barrel distortion, rectilinear lenses render parallel lines correctly and with minimal, if any, levels of distortion.
Wide-angle lenses have angles of view of 84° to 64°. For full-frame cameras, this translates to lenses from 24mm to 35mm, or 15mm to 22mm for APS-C format cameras. Ultra-wide-angle lenses are defined as lenses with angles of view greater than 84°. For full-frame and APS-C format cameras, Canon offers a choice of 20mm (94°/58° FOV) and 14mm (114°/71° FOV) fixed focal length lenses, as well as a 15mm full-frame fisheye (180°).
Fisheye lenses can also be divided into two categories: circular and diagonal fisheyes. Circular fisheyes, which capture fields of view (FOV) of 180° or wider, are readily recognizable by their round image fields. Diagonal fisheye lenses, which typically take in FOVs of 114° to 180°, capture fields of view of up to 180°, but fill the entire frame.
Unlike standard lenses, which render scenes much as we see our surroundings as our eyes see things, wide-angle pictures have a greater sense of depth. Perspective is also altered, and spatial relationships between subjects located at different distances from the lens appear further apart than they actually are, much like the warnings on our cars' side-view mirrors inform us.
These spatial distortions can be used creatively, depending on how the camera is positioned in relation to the subject. As an example, a common stone can appear monumental when photographed close-up at eye-level with a wider-angle lens. The word "dramatic" is often used to describe photographs captured using wide-angle lenses.
Wide-angle lenses are commonly used in commercial applications in which part of a product—or the product itself—is highlighted and set apart from its surroundings by focusing in tightly with a wider-angle lens. Wide-angle lenses are indispensable when photographing interiors and smaller spaces. It should be noted that when shooting with wider-angle lenses indoors, interior spaces often appear larger than their actual dimensions, a fact that is not ignored by real estate agents. The obvious uses for wide-angle lenses are landscapes and interiors, but when used thoughtfully, wide-angle lenses can be used for many applications, including portraits.
For architectural and landscape photographers, these lenses are truly invaluable. In the creative arena, ultra-wide-angle lenses make it possible to view physical spaces and their surroundings from any number of perspectives. In the right hands, ultra-wide lenses make it possible to create photographs that cause the viewer to stop in their tracks for a closer view.
Useful in any number of situations and environments, the 28mm focal length is probably the most popular choice among wide-angle enthusiasts for its ability to be a wide-angle lens without visually screaming WIDE ANGLE, FOLKS! In the 28mm range (75°/ 47° FOV), Canon offers two choices: an image-stabilized EF 28mm f/2.8 IS USM and a wider-aperture EF 28mm f/1.8 USM that’s not image-stabilized, but is 1.3 stops faster.
Canon also offers a choice of three 35mm lenses (63°/39.3°): an L-series EF 35mm f/1.4L USM, an EF 35mm f/2 USM, and an EF 35mm f/2 IS USM, all of which get extremely high marks among Canon users.
What attracts many shooters to 35mm lenses is that much like a 50mm lens, the 35mm doesn’t monkey with perspective that much, but manages to take in more of the immediate surroundings around the main subject than a 50mm lens would. And because it has a slightly wider field of view compared to a standard lens, the viewer becomes drawn into the story. This is one of the reasons journalists have long praised 35mm lenses.
Standard lenses
Normal, or standard, lenses fill the void between 36mm and 60mm on a full-frame camera (62° to 40° AOV), or 22.5mm to 37.5mm on an APS-C-format camera.
Canon offers a wide choice of normal lenses, ranging from an entry-level 50mm f/1.8 through a faster 50mm f/1.4 and faster-yet 50mm f/1.2 for extreme low-light shooting and/or narrow-range selective focus.
Unlike wide-angle lenses, which seemingly expand spatial distances between subjects located at varying distances from the camera position, and telephoto lenses, which perceptually flatten the space between subjects situated at varying distances from the lens, normal lenses record the scene to closely resemble the way our eyes perceive the scene.
Essentially, normal lenses don't play games with our sense of depth perception, or to quote naturalist and professional fly-fisherman Alan Kessel, "they’re honest.”
If you were to photograph two people, one standing 3' from the camera and the other 6' from the camera, using a standard lens on the camera, regardless of format, the perceived distance between them would appear correctly proportional. This, along with the comparably wider maximum apertures common to normal lenses, is what makes them desirable among journalists and others who prefer to record their subjects in, optically speaking, a straightforward manner.
Short and medium telephoto lenses
Camera lenses with angles of view between 30° and 10° are referred to as standard or short telephoto and medium telephoto lenses. On a full-frame camera, these lenses range from 85mm to 135mm, or about 50mm to 85mm on an APS-C format camera. Just as a 35mm lens is "slightly wider" than a normal lens, an 85mm lens is slightly tighter than a normal lens.
Portrait and fashion photographers prefer lenses in this category because they lend a small measure of compression to facial features that is pleasing to the eye. The slightly narrower AOV of these lenses also serves to isolate the subject from its surroundings, especially when shooting at the notably fast (f/1.2, f/1.8, and f/2) maximum apertures found on Canon's selection of short and mid-range telephotos.
For fashion and beauty photographers, Canon’s EF 85mm f/1.2L II USM is ideal for classic portrait use as well as extreme degrees of selective focus when used close up at its widest aperture. Even at further distances, the selective focus abilities of the EF 85mm f/1.2L II USM is unsurpassed in its class.
And for shooters on more modest budgets, Canon’s EF 85mm f/1.8 USM features many of the attributes of its faster L-series sibling at a price point that should appeal to pros and enthusiasts alike. Both of these lenses feature a FOV of 28° on a full-frame camera, and 17.5° when used on APS-C-format cameras.
Canon offers two additional lenses in this category: the EF 100mm f/2 USM (24° full-frame, 15° APS-C), which like Canon's 85mm offerings, is designed for portraits and other short-telephoto needs, and the well-regarded EF 135mm f/2L USM (18°, 11.25°), an L-series lens considered to be one of Canon’s best camera lenses in terms of resolving power and overall image quality.
Telephoto and super telephoto lenses
Canon breaks their longer telephotos into two specific categories: telephoto, which in the case of full-frame cameras includes lenses from 135mm to 300mm, and super telephoto, which includes lenses 300mm and longer. Regardless of how they are categorized, the definition of a telephoto lens is a lens with an angle of view narrower than 35°. Super telephotos have angles of view that start at 8° and narrow to 3°5' on an 800mm lens.
Just as wide-angle lenses capture subjects and their surroundings, telephoto lenses, when used at closer distances and widest apertures, can isolate the subject from its surroundings. I mention closer distances because when focused on distant subjects, telephoto lenses seemingly compress the physical distance between the subject, its foreground, and background.
In the case of telephoto lenses 400mm and longer, multiple objects within a scene separated by distances of hundreds of yards can appear as if they are stacked one against the other due to the image-compressing characteristics of longer telephoto lenses.
Visually speaking, telephoto lenses are the yang to the wide-angles' yin. One captures wide expanses, the other reaches into the details. One seemingly places greater distance between subjects within the frame, the other brings them closer together.
Long lenses and stability
If you’ve ever peered through a pair of binoculars, you know how difficult it can be to hold them steadily enough to clearly see the distant subject you’re trying to view. Similarly, one of the challenges of shooting with telephotos is stabilizing them. As a rule, you shouldn’t try to handhold a lens at a shutter speed slower than its focal length (a 500mm lens no slower than 1/500, a 50mm lens no slower than 1/50, etc.).
A tripod (the sturdier the better) is the best method of eliminating camera shake. If handholding is the only option, a majority of Canon’s telephoto lenses are image stabilized, which makes it possible to drop the shutter speeds by up to 4 stops.
Many of Canon’s telephotos also feature wide maximum apertures, which in turn also enable faster shutter speeds. Faster telephoto lenses are larger, heavier, and pricier than their smaller-aperture counterparts, but the payoff is in their ability to capture sharp images under more difficult lighting conditions.
Canon produces a choice of 11 fixed focal length telephoto and super-telephoto lenses, and the industry's only zoom telephoto lens with a built-in 1.4x teleconverter.
As for speed, fast maximum apertures can be found on each of these high-performance lenses. There’s a super-fast EF 200mm f/2L IS USM, as well as an EF 200mm f/2.8L II USM, 300mm L-series lenses with maximum apertures of f/2.8 and f/4, a trio of 400mm lenses with maximum apertures of f/2.8, f/4, and f/5.6, an EF 500mm f/4L IS II USM, an EF 600mm f/4L IS II USM, and an EF 800mm f/5.6L IS USM that can be handheld.
Perhaps the most advanced, and certainly the most optically flexible long lens offered by Canon is the EF 200-400mm f/4L IS USM Extender 1.4x, which as its name suggests, features a 1.4x extender that can be engaged at any time by simply flipping a switch on the lens barrel.
Without the 1.4x extender in place, the lens is a nimble 200-400mm f/4 zoom. Flip the extender and the lens transforms into an equally nimble 280-560mm f/5.6 zoom. For shooting sports and other fast-action subjects from a distance, this lens is a godsend.
What each of these lenses share are various combinations of aspheric, Fluorite, UD, and Super-UD glass, rear focusing, SWC lens coatings, and weather-resistant magnesium-alloy construction.
"Kit" zooms
Many cameras are available with 18-55mm kit zooms, which typically feature 35mm equivalent focal-length ranges of about 28.8mm to 88mm on APS-C format cameras. Depending on the camera model, kit zooms might be a bit wider than this on the short end of the focal range, or a bit longer on the telephoto side.
What you get for your money is a lens that can capture angles of view about twice as wide as a normal lens to about twice as long as a standard lens. Kit zooms are excellent lightweight starter lenses for those first learning the intricacies of camera lenses. Kit zooms are also ideal for casual, one camera/one lens day tripping.
Wide and standard zoom lenses
In the extreme wide zoom category, Canon is the only company that offers a fisheye to ultra-wide zoom lens, the EF 8-15mm f/4L Fisheye USM. This amazing L-series lens can zoom out to a 180° circular image on full-frame cameras or 180° full-diagonal screen on an APS-C format camera.
Other features of this lens include UD glass elements for better control of chromatic aberrations, floating elements for sharper edge detail when focusing close up (down to 6.2"), a rear, 3-slot gel holder, SWC coatings, and a special Fluorine coating to repel smears and fingerprints from the front element.
Canon manufactures four wide zooms, three of which are L-series EF lenses for use with full and cropped sensors, and all of them fit easily into carry-on baggage.
For APS-C DSLRs, Canon offers the EF-S 10-22mm f/3.5-4.5 USM, which covers the focal range of a 16-35.2mm (35mm equivalent) lens (107°30' to 63°30' AOV). The EF-S 10-22mm f/3.5-4.5 USM features three aspherical lens surfaces, a Super-UD element, focusing down to 9.5", and USM AF-assist.
For full-frame cameras, Canon's wide zoom arsenal includes the EF 16-35mm f/2.8L II USM (108°10'-63°AOV) and the EF 17-40mm f/4L USM (104°-57°30' AOV), which is a stop slower, about 20% lighter in weight, and about half the price of the EF 16-35mm f/2.8L II USM; both are high-performance L-series lenses.
Canon currently manufactures 12 Standard Zooms, eight of which feature EF-S mounts exclusively for use with Canons APS-C format DSLRs. With the exception of the constant-aperture EF-S 17-55mm f/2.8 IS USM, each of these lenses features variable apertures that range from f/3.5 at the wide-angle side to f/5.6 at the telephoto end of the focal range.
On the wide end of their focal ranges, each of these lenses starts at 15mm to 18mm (84°30' to 74°20' AOV) and go as long as 55mm to 200mm (27°50' to 7°50' AOV). All of the Canon EF-S in this group are image-stabilized and many are USM-equipped for quick autofocus action. Canon’s newest kit zoom, the EF-S 18-55mm f/3.5-5.6 IS STM, features an STM AF motor in place of a USM drive.
For full-frame cameras, Canon offers a choice of four EF-series zooms, three of which are L-series optics: the EF 24-70mm f/2.8L II USM, EF 24-70mm f/4L IS USM, and EF 24-105mm f/4L IS USM, with full-frame angles of view of 84° through 34° (70mm) or 23°20' (105mm). The fourth lens is an EF 28-135mm f/3.5-5.6 IS USM (75°-18° AOV). With the exception the EF 24-70mm f/2.8L II USM, each of these lenses is image stabilized and can also be used on any of Canon’s APS-C DSLRs.
Telephoto zoom lenses
Canon offers a total of 13 tele-zooms ranging from L-series all-in-one zooms, such as the EF 28-300mm f/3.5-5.6L IS USM (75° to 8°15' AOV) that can capture almost anything that comes your way, to faster, classic Canon zooms such as the EF 70-200mm/f2.8L USM (34° to 12° AOV) and its image-stabilized sibling, the EF 70-200mm f/2.8L IS II USM. 11 Canon zoom lenses have EF mounts and two are strictly EF-S, for use with APS-C DSLRs.
An interesting aspect of Canon's lenses, fixed focal length and zoom, are the choices Canon offers their customers. As an example, Canon manufactures four 70-200mm L-series zoom lenses. Two have maximum apertures of f/2.8 for those who require maximum performance under lower lighting conditions, and two smaller and lighter versions with maximum apertures of f/4 (1 stop slower). Each of these excellent zooms is available with or without image stabilization, and Canon offers similar options in other lens categories.
Tilt-shift lenses
Canon TS-E tilt-shift lenses offer DSLR shooters the ability to shoot architectural and product assignments with the tilt-and-shift controls comparable to the controls formally available only on larger-format view camera systems.
Canon TS-E lenses are manual focus only, due to the complexity of tilt-shift lens designs, but they do offer fully automatic diaphragm control, UD glass, and aspheric elements for minimizing aberrations, rear focusing, eight rounded-iris diaphragm blades for natural-looking out-of-focus details, solid, weather-proof construction, and SWC lens coatings.
It’s important to keep in mind the tilt-shift controls made possible by these lenses are not limited to commercial and technical assignments, but can be put to good use in creative, fine art applications.
Canon offers a choice of four TS-E tilt-shift lenses, the widest being the TS-E 17mm f/4L, which makes it possible to capture incredibly dramatic interior and exterior photographs. The TS-E 17mm is also a terrific tool for photographing architectural models and product photography.
In addition to the TS-E 17mm f/4L, Canon also produces the TS-E 24mm f/3.5L II wide-angle, a TS-E 45mm f/2.8 normal lens, and a TS-E 90mm f/2.8 short telephoto. All of Canon's TS-E lenses have the ability to tilt and shift the vertical plane of focus by +/- 90° along with a +/- 8.5° range of movement.
Many software applications have "perspective control" functions that can correct keystone distortion; the corrections are electronic and the resulting files contain interpolated image data. These same distortions corrected in-camera using TS-E lenses are optically corrected, and contain no traces of made-up image data. In terms of fine image detail, no electronic interpretation of data can replicate the levels of detail you only get from a high-quality lens.
Macro lenses
Many non-macro lenses feature close-focusing abilities, which while valuable in expanding the imaging abilities of the lens, should not be confused with the highly corrected, sharp edge to edge, flat-field images you can only get from a true macro lens. Unlike conventional lenses, macro lenses are unsurpassed when it comes to high levels of resolving power across the entire image field, even at the closest focusing distances.
Canon has one of the most extensive selections of macro lenses in the industry. Designed to record exacting detail at magnifications ranging from half life size through 5x magnifications, and in a choice of focal lengths ranging from 50mm through 180mm, there’s a Canon macro lens available for any close-up assignment you might encounter.
For extreme, highly detailed close-ups, Canon offers the MP-E 65mm f/2.8 1-5x Macro lens, which can manually focus down seamlessly to five times life size without the need of extension tubes, making it indispensable for any number of industrial, commercial, and fine-art applications.
While it might seem redundant to offer a half-dozen lenses that can focus down to half or full life size, it’s important to keep in mind it’s not always possible to get close to wildlife subjects, tightly-lit studio setups, and situations in which the camera, the lens, or the person behind the camera casts a shadow on the subject. And just as the focal length of a conventional lens affects the visual characteristics of a picture, the same holds true for macro lenses.
Depending on the lens, Canon's macro lenses feature lifesize (or half life size) reproduction ratios, circular diaphragm blades, manual-focus override for critical focusing, USM focus drives, image stabilization, inner-focusing, floating elements, and UD glass elements.
To enable life-size imaging with Canon's EF 50mm f/2.5 Compact Macro, which only focuses down to half life size, Canon manufactures the Life-Size Converter EF (4-elements in 3-groups), which increases the magnification ratio of the EF 50mm f/2.5 Compact Macro to full 1:1 life size.
Canon EF extenders
Lens extenders are a cost-effective, space-saving method of expanding the focal range of your existing lenses without having to expand the size of your camera bag. To extend the focal ranges of select Canon EF-series lenses, Canon offers the Extender EF 1.4x III, which magnifies the focal length of the lens by 1.4x, and the Extender EF 2x III, which doubles the focal length of select Canon EF-series lenses. Both Extenders retain full AF functionality when used with compatible Canon EF-series lenses.
The Extender EF 1.4x III contains 7 elements in 3 groups, magnifies the focal length of the lens by 40%, and reduces the effective aperture of the lens by 1 stop. The Extender EF 2x III doubles the focal length of the lens and reduces the effective aperture of the lens by 2 stops. The Extender EF 2x III, which contains 9 elements in 5 groups, features a built-in microcomputer for seamless communication between the camera, extender, and the lens.
In addition to the weatherproofing and construction attributes of the Extender EF 1.4x III, the Extender EF 2x III also features Fluorine lens coatings for better smudge and fingerprint resistance.
The Canon Extender EF 1.4x II and Extender EF 2x III are only compatible with fixed focal length L-series lenses 135mm and longer, as well as the EF 70-200mm f/2.8L, EF 70-200mm f/2.8L IS, EF 70-200mm f/4L, and the EF 100-400mm f/4.5-5.6L. Additionally, please see the lens or camera body manual for full compatibility information.
Canon EF-M lenses
There are currently two EF-M lenses available for the Canon EOS M series mirrorless cameras: an EF-M 18-55mm f/3.5-5.6 IS STM, and an EF-M 22mm f/2 STM pancake lens.
The EF-M 18-55mm f/3.5-5.6 IS STM is the kit lens for Canon’s EOS M camera. Modestly smaller and lighter than its EF-S mount counterpart, this 28mm to 88mm equivalent zoom lens features a video-friendly STM AF motor, 4-stops of Dynamic image stabilization, and an inner focusing design.
A smaller (only 0.9" thick) and faster lens option is the EF-M 22mm f/2 STM, a 35mm equivalent pancake lens that features a circular 7-blade aperture, silent STM drives for noise-free video capture, and close focusing down to 5.9".
Summary
Lenses do not make for a simple subject, nor are they items you should purchase serendipitously. Whether you’re an avid enthusiast or a working professional, you will most likely be replacing and updating camera bodies with far more frequency than your lenses, which means when purchasing lenses, it’s important to be clear about your needs and expectations. By doing so, you will be more likely to fill the lens compartments of your camera bag efficiently with lenses that will do the job you need to do.
The reputation of Canon EF-series lenses is built upon a number of strong points; key among them is Canon's dedication to providing lenses in all focal ranges—fixed focal-length and zoom—that fit the performance and budgetary needs of their entire customer base, pros and enthusiasts alike. With decades of experience and feedback from generations of professional shooters and avid enthusiasts, Canon has both set and maintained a standard of quality that is respected throughout the industry.
