Canon SLR Lenses

Earlier Canon SLR lenses (pre-1987) were fitted with a mechanical lens mount and carried the designation "FD". These lenses were made for Canon's older 35mm SLR (single lens reflex) film cameras like the highly-rated Canon AE-1 and Canon A-1 bodies.

The FD lenses were replaced in 1987 with EF (electro focus) lenses fitted with electronic mounts, allowing seamless integration with the camera's electronic shutter and metering system. The EF designation remains in use today and these lenses can be used with any of the following Canon SLR cameras:

1. Canon 35mm film cameras (Canon EOS models, although only the EOS 1v is still manufactured)
2. Canon full-frame digital SLR cameras (Canon EOS 1Ds, 1Ds Mk II, 1Ds Mk III, 5D, and 5D Mk II)
3. Canon digital SLR cameras with APS-H sensors (Canon EOS 1D, 1D Mk II, 1D Mk III, and 1D Mk IV)
4. 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).

Canon also manufacture a range of SLR lenses made specifically for its cameras with the smaller APS-C sensors.

The image cast by an EF lens fills a 36 x 24mm rectangle, which is the size of a normal 35mm negative or full-frame sensor. When the same lens is fitted to a camera with a smaller, 22.5 x 15mm APS-C sensor, the image fills more of the rectangle.

The effect in the viewfinder, and on the sensor, is like using a 1.6x teleconverter, or 60% longer lens. This causes wide angle lenses to lose their impact, making them more like standard lenses, e.g. a 28mm lens x 1.6 = 44.8mm.

More Wide Angle Choice

To provide photographers using digital SLRs with APS-C sized sensors with more wide angle choice, Canon developed a new EF-S mount and range of matching EF-S lenses.

While EF lenses can be used on all Canon's digital SLR bodies, the EF-S lenses are designed exclusively for use on cameras with the smaller sensor. You cannot, for example, use a Canon EF-S 18-55mm zoom lens on a full-frame Canon 5D or 1Ds camera.

Canon's huge range of SLR lenses (more than 60, from fish-eye to super telephoto) can also be categorized into:

• Prime or fixed-focal lenses, and
• Zoom or variable focal length lenses

Zoom lenses, because of their incredible versatility and value for money, are the first choice for most photographers, particularly amateurs. Instead of carrying a bag full of prime lenses, a photographer can carry two zoom lenses that cover from wide angle to telephoto, e.g. Canon EF 24-70mm f/2.8L USM plus Canon EF 70-200mm f/2.8L IS USM or, in the case of EF-S lenses, the Canon EF-S 18-55mm zoom plus Canon EF-S 55-250mm f/4-5.6 IS zoom (equivalent focal length on a 35mm camera of both lenses is 28 to 400mm!).

Advances in lens technology have also seen great strides in the image quality provided by zoom lenses which, in some cases, is nearly the equal of that provided by prime lenses.

Professional photographers nevertheless still opt for prime lenses where possible, mainly because of their faster maximum aperture, allowing use in low light. No zoom lens of similar focal length can equal the f/2.8 aperture of Canon's EF 400mm f/2.8L IS USM or the EF 600mm IS USM lens's f/4 maximum aperture.

Similarly, Canon's prime wide angle and standard (50mm) lenses offer unrivalled image quality at wide maximum apertures.

L-Series Lenses

Canon's top-of-the-range SLR lenses carry the "L" designation and are distinguishable by the red circle around the lens barrel. These professional lenses offer the ultimate in image quality, with protection against weather and aging and include special optical materials such as fluorite, ultra-dispersion (UD) or super UD elements.

Other Canon SLR lens codes include the following:

• IS -- refers to image stabilizer. Image stabilizer lenses detect and compensate for unwanted movement, allowing for the use of shutter speeds up to three stops slower than would otherwise be possible.
• USM -- ultra sonic motor. Technology pioneered by Canon to produce highly responsive, super fast focusing with excellent holding torque.
• DO -- indicates the use of multi-layer Diffractive Optical elements. This revolutionary technology, unique to Canon, enables the manufacture of smaller, lighter and outstanding performance photo lenses.
• TS-E -- specialist tilt/shift lenses that allow correction of perspective distortion and control over the the focus range. These lenses are often used for architectural interiors and exteriors.