Canon EF 70-200mm F/4L IS USM telephoto zoom lens

Canon EF 70-200mm F/4L IS USM Zoom Lens

There are more than 60 Canon SLR lenses available for Canon EOS single lens reflex cameras. This can be daunting for a beginner photographer trying to find the appropriate lens for a digital SLR like a Canon 450D.

This is a typical description for a Canon SLR lens: “Canon EF 70-200mm f/4L IS USM”. You’ll notice the various letters or codes in the description that need to be understood such as EF, L, IS, USM.

Here’s a brief rundown of Canon codes or designations:

1. “EF” designation

Canon introduced a new range of SLR lenses for its EOS 35mm film cameras around 1987. These “electro-focus” lenses had electronic mounts and replaced the existing range of FD lenses.

Today EF lenses remain the core of Canon’s lens lineup and can be used with older 35mm film cameras, top of the range full-frame digital SLRs like the Canon EOS 1Ds Mk III and entry-level cameras like the Digital Rebels (300D to 500D)

2. “EF-S” designation

Canon’s entry-level Digital Rebels and its prosumer 20D to 50D cameras have what’s called an APS-C format sensor which, at 22.5 x 15mm is smaller than a full-frame sensor (36 x 24mm).

The smaller sensor has the effect of cropping the image, known variously as “crop factor” or “lens magnification factor” and is similar to using a 1.6x converter. (See our previous post, Canon Digital SLR Crop Factor, for more on this).

While this is a bonus when using a telephoto lens — your 200mm lens now acts like a 320mm lens — it’s a disadvantage when shooting with wide angles. In the latter case, a really wide lens like a 24mm now becomes longer by 1.6x, so is like using a 38.4mm lens.

To counter the effect of crop factor on wide angle lenses, Canon introduced its EF-S lenses specifically for 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.

3. “IS” designation

This stands for “image stabilization”, a technology aimed at reducing the camera shake that results in unsharp images. Each IS lens has its own image stabilizer unit, comprising a microcomputer and two vibration gyros, which detects lens movement and rectifies this.

4. “USM” designation

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.

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 lens lineup.

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

6. “DO” designation

Stands for Diffractive Optics — an optical technology developed by Canon for building telephoto lenses that are significantly shorter and lighter than previously possible. 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.

For a more in-depth discussion about Canon lenses and what the various codes and designations mean, see this Squidoo lens: Canon SLR Lenses and All You Need to Know