Canon SLR Lenses and All You Need to Know About Them

Single lens reflex (SLR) cameras have inter-changeable lenses, making them extremely versatile tools. A single camera body and a wise selection of lenses will give you a massive range of focal lengths -- from ultra wide angle to super telephoto -- allowing you to shoot virtually any subject you choose. This versatility, plus superior image quality, is what sets SLR cameras apart from compact digital cameras.

Canon and Nikon are the leading manufacturers of SLR cameras and these brands are invariably the choice of professional photographers. I'm not a camera junkie and I'm certainly not passionately attached to one brand -- at various times in my life I've used and owned Olympus, Minolta, Nikon and Canon SLRs, plus Hasselblad, Pentax and Mamiya medium-format cameras.

However, for the past 10 years or so I have been using Canon SLRs, so this is strictly about Canon lenses for use on Canon SLR cameras (film and digital).

The problem for anyone starting out with a Canon SLR is the vast array of Canon lenses available. Add a string of identifying codes and it becomes very confusing deciding which lenses are suitable for specific cameras and photographic applications.

Here's a typical Canon lens description: "Canon EF 70-200mm f/2.8L IS USM" -- where we have EF, L, IS, and USM designations to decipher.

The 70-200mm covers the focal length of this zoom lens, while the f/2.8 indicates its maximum aperture. These identifiers of focal length and maximum aperture are common to all lens brands, so won't be discussed in further detail. It's the designations specific to Canon we need to understand.

1. "EF" designation

To see the bigger picture, we need to go back a few years, before digital cameras existed. In 1987 Canon introduced a new range of SLR lenses for its EOS 35mm film cameras. These EF (electro-focus) lenses had electronic mounts and replaced the existing range of FD lenses fitted with mechanical mounts.

Twelve years on and "EF" remains the main identifier for Canon's core lineup of SLR lenses. There are more than 60 EF lenses available and they're both backward and forward compatible, so the latest ones can be used on older EOS film cameras, while a lens produced 10 years ago will work on the newest EOS digital SLR like the 7D.

The "EF" designation is commonly used immediately after the word "Canon" in the description, so you know straight off that it's part of the core range and will fit any of the following Canon EOS bodies:

a) Canon EOS 35mm film cameras (Only the EOS 1v is still manufactured)
b) Canon full-frame digital SLR cameras (Canon EOS 1Ds, 1Ds Mk II, 1Ds Mk III, 5D, and 5D Mk II)
c) Canon digital SLR cameras with APS-H sensors (Canon EOS 1D, 1D Mk II, 1D Mk III, and 1D Mk IV)
d) Canon digital SLR cameras with APS-C sensors (Canon Rebel series {300D, 350D, 400D, 450D, 500D and 1000D}, plus 10D, 20D, 30D, 40D, 50D, and 7D).

2. "EF-S" designation

Canon digital SLR cameras use a sensor instead of film to record the image. The EF lenses mentioned above were introduced prior to the advent of digital cameras and were designed for 35mm film cameras. This meant the image they cast had to fully cover a piece of 35mm film, which is 36 x 24mm in size.

A "full-frame" digital sensor is the same size as a piece of film, so the image cast by an EF lens when fitted to a camera with a full-frame sensor fills the sensor exactly as it does with film.

Sensors however are expensive to manufacture. To make digital SLR cameras affordable for amateur photographers, camera manufacturers opted to produce entry-level and prosumer digital SLRs with smaller sensors. In Canon's case, this is the Digital Rebel series (300D to 500D) and 20D to 50D plus 7D. All these cameras have what is called an APS-C format sensor that measures 22.5 x 15mm -- substantially smaller than a full-frame sensor.

When you couple a camera with the smaller APS-C sensor to an EF lens, the implications are far-reaching. Now the image cast by the lens is too big for the sensor and "overflows". It's as if you've cropped the image, chopping off the top, bottom and sides. This effect is known variously as crop factor, lens magnification factor, or focal length conversion factor.

In the case of Canon's entry-level and prosumer models, the crop factor is 1.6x -- similar to using a 1.6x converter on the lens. So a 200mm lens produces a similar level of magnification and angle of view as would a 320mm lens on a 35mm film or full-frame digital camera (200 x 1.6).

This is great for photographers using telephoto lenses, as the lenses act as if they have 60% additional magnification. A reasonably priced tele lens like the EF 70-300mm f/4-5.6 IS zoom now mimics a 112-480mm zoom lens, which is a huge bonus for sport and wildlife photographers.

But the crop factor is similarly very limiting for those who use wide angle lenses. A 24mm lens, so useful on a 35mm film camera, now equates to a 38.4mm on a Canon 50D -- not exactly exciting and more akin to a standard lens.

To overcome this limitation, Canon introduced an additional range of lenses specifically for its digital SLRs with APS-C format sensors. These carry the "EF-S" designation and cannot be used on EOS film cameras or on full-frame digital cameras like the EOS 1Ds. (Note -- Canon EOS 1D cameras have a sensor with a 1.3x crop factor and EF-S lenses also cannot be used on them).

Although EF-S lenses are made to counteract the crop factor effect, it's important to understand that the crop factor still applies. The camera's sensor is still smaller than full-frame, so the image will still appear magnified. For this reason "equivalent" focal length is used when describing EF-S lenses. Thus the EF-S 10-22mm lens, which would be impossibly wide for a 35mm film camera, has an equivalent or apparent focal length of 16-35mm when fitted to a Rebel XTi or 50D body.

There are currently 10 Canon EF-S lenses available (nine zooms and one macro lens), covering mainly wide angle focal lengths. They are generally lighter and more compact than EF lenses.

3. "IS" designation

IS stands for "image stabilization", a technology aimed at reducing the camera shake that results in fuzzy, unsharp photographs. Canon IS lenses help reduce this camera shake, resulting in sharper images.

How does IS work? Canon explains that camera shake during exposure causes the lens to move, which in turn shifts the angle of incoming light relative to the optical axis, resulting in blurred photos.

The image stabilizer unit, comprising a microcomputer and two vibration gyros, detects lens movement and rectifies this by shifting certain optical components within the lens in inverse relation to the lens movement. This maintains the position of incoming light rays on the camera's sensor, so helping eliminate blur caused by lens movement.

Canon introduced the first interchangeable 35mm SLR camera lens with camera shake compensation in 1995 -- the EF 75-300mm f/4-5.6 IS USM lens. Canon has subsequently improved the stabilization performance, resulting in new IS lens designs.

4. "USM" designation

USM stands for ultra sonic motor. USM technology, pioneered by Canon, uses sound waves to position the lens elements when focusing to produce highly responsive, fast and silent focusing with excellent holding torque.

According to Canon, USM lenses draw minimal power from the camera, ensuring longer battery life. Canon makes two types of USM lenses:
* Ring-type USM lenses, found in large aperture and supertelephoto designs, that permit manual focusing without first switching out of auto mode;
* Micro USM designs that bring the performance benefits of USM technology to a wide assortment of affordable Canon lenses.

5. "L" designation

Canon L lenses are designed for professional use, carry the "L" designation in the description, and have a red ring around the lens barrel to distinguish them from Canon's normal lenses. Canon sometimes refers to these lenses as "luxury" lenses and it's popularly accepted "L" stands for luxury.

L lenses are made with special optical materials such as fluorite, ultra-dispersion (UD) or super UD elements to produce images that are sharp and clear with superior color rendition.

As these lenses have to withstand the rigors of professional use and keep out dust and moisture, they are made with rubber seals at interface areas such as switch panels, exterior seams and lens mounts.

6. "DO" designation

DO stands for Diffractive Optics -- an optical technology developed by Canon for manufacture of telephoto lenses that are significantly shorter and lighter than previously possible, while improving optical performance by reducing chromatic aberration. Canon produce two DO lenses, the EF 70-300mm f/4.5-5.6 DO IS USM zoom lens and the EF 400mm f/4 DO IS USM telephoto lens.

7. "TS-E" designation

TS-E are specialist tilt/shift lenses that allow correction of perspective distortion and control over the focus range, used mainly for architectural interiors and exteriors.

8. "Macro" designation

Denotes a Canon macro lens, also known as a close-up lens. Macro lenses have the ability to focus an image on the film or sensor that is at least as large as the subject - i.e. a magnification of 1:1.

See also:
Canon Crop Factor
Canon Telephoto Lenses
Canon Zoom Lenses
Canon Wide Angle Lens
Canon EF Lenses
Canon IS Lenses

Here's a list of my web sites, plus links and info about a number of nature and photography sites I enjoy and recommend.

• Wildlife Pictures Online -- My primary web site, containing hundreds of wildlife pictures plus wildlife and photography articles, stock images and free wildlife pics for personal or commercial use.
  
• Wildlife Photography Blog -- Here you'll find captivating, unexpected, and constantly updated wildlife and nature pictures that'll bring the excitement of untamed Africa to your doorstep......plus news and views on wildlife and conservation; photography and equipment; safari and travel destinations.
  
• Scotch Macaskill's Blog -- A personal blog about photography, wildlife, and living in Africa - where I post pictures that appeal to me and that I enjoyed making, including some of my more experimental and playful images.
  
• Widllife Stock Pictures -- Affordable wildlife stock images starting at just $7 each sold with royalty free license
  
• Posters and Fine Art Prints -- An outstanding selection of affordable posters and fine art prints covering the following subjects: Movies, Music, Fine Art, Cars, Animals, Travel, Sport, and Hot Girls - plus related, relevant articles and news.
  
• Hiking Basics -- About hiking gear, trails, and how to enjoy your hiking - with articles from hiking enthusiasts and equipment experts, plus featured and top-selling hiking gear from Amazon.com
  
• The Luminous Landscape -- Michael Reichmann's superb site devoted to the art of landscape, nature and documentary photography using digital as well as traditional image processing techniques.
  
• Bob Atkins Photography -- A valuable resource, particularly for Canon users, Bob Atkins's site has information on the Canon EOS system, in-depth camera and lens reviews, articles, plus image galleries and digital photography news.
  
• Naturescapes -- Another excellent nature photography resource - offering articles, workshop listings, galleries, a members' area, and comprehensive forums.
  
• Nature Photographers Magazine -- Superb online magazine that features a cover shot to make you weep with jealousy and offers in-depth instruction on wildlife and nature photography, plus galleries, forums and photo tips.
  
• Canon Product Finder -- Find the Canon home product you need - from Canon UK's website.
  
• Right Canon Lens for the Job -- Helpful tips and suggestions as well as some recommendations for Canon lenses that will help you accomplish your goal.