The actual product names of individual Canon lenses are fairly easy to decipher; they’ll include either the EF or EF-S designation, the focal length or focal length range of the lens, its maximum aperture, and some other information. Additional data may be engraved on the barrel or ring surrounding the front element of the lens, as shown in Figure 6.3. Here’s a decoding of what the individual designations mean:
EF/EF-S. If the lens is marked EF, it can safely be used on any Canon EOS camera, film or digital. If it is an EF-S lens, it should be used only on an EF-S compatible camera, such as the Digital Rebels, EOS 20D/30D/40D, and any newer APS-C cameras introduced after the publication of this book.