Understanding the Differences Between Canon’s EF and EF-S Lenses

It’s been a while since I posted this article the first time so I thought it time to clear up a little misinformation I’ve seen floating around the web lately.

What is this Field of View Crop Factor (1.6x FOVCF) everyone keeps talking about and how does this affect my lens choices for the Canon DSLR cameras?

As you know the sensor in the new Rebels, EOS 60D and EOS 7D are much smaller than the full frame sensor found in Canon’s high-end DSLRs like the EOS 5D Mark II and 1D Mark IV. The physical focal length is a optical measurement of a lens and does not change just because you mount it on a 1.6x FOVCF camera like the 60D or 7D, but the field of view the lens exhibits certainly does.

For example, if you are looking for a field of view that a 50mm lens provides on a full-frame DSLR body like the 5D Mark II, you’ll probably want a 35mm lens on your 60D since 1.6 x 35mm = 56mm. The lens is still a 35mm lens, but the final image captured by your 60D will only include a crop of the lens’ complete image.

Wildlife photographers really love the benefit of using high crop factor (1.6x) DSLRs like the 60D or 7D since they can achieve tight subject framing from a greater distance or from the same distance with a shorter, less expensive lens. Using an EF 500mm f/4 L IS USM telephoto lens on a 60D yields the same field of view as an 800mm f/4 IS USM lens would on a 5D Mark II.

So where does the EF-S lens fit in this?

Canon developed the EF-S series lenses (the “S” stands for short back focus) with the rear element of the lens closer to the image sensor than on the EF series lenses. They also matched the image circle of these lenses to the APS-C sensor size. This design enables EF-S lenses to be made smaller, lighter and less expensive. A perfect match for their consumer and prosumer grade DSLR cameras.

Comparing Canon's EF and EF-S Lenses

Canon EF-S lenses are designed specifically for the 1.6x FOVCF DSLR bodies but still require the same 1.6x crop factor to be applied as the standard Canon EF Lenses to get the equivalent field of view comparison. Again, this is because the physical focal length of the lens is the same, regardless of which camera it’s mounted on.

The Canon EF-S 10-22mm f/3.5-4.5 USM is a great example of a well designed EF-S series lens. It provides a field of view similar to what Canon’s popular EF 16-35mm f/2.8 L II USM and EF 17-40mm f/4.0 L USM do on a full frame camera like the 5D Mark II.