Canon Telephoto Lenses »
The Canon EF 200mm f/2.8L II telephoto lens is a popular, low-cost alternative to expensive zoom lenses. While it does not have the versatility of a zoom lens, it does offer exceptional image quality,Read More »
The Canon 300mm f/2.8L IS USM telephoto lens might just deliver the best image quality of any Canon lens. While this is a matter subject to a great deal of opinion, it is clearRead More »
About Canon Telephoto Lenses
To understand what telephoto lenses are all about, one has to understand the concept of “focal length.” The “focal length” of an optical system is a measure of how strongly the system converges (focuses) or diverges (defocuses) light. As a matter of fact, it is the distance over which collimated light is brought to a focus. By convention a normal lens on a 35mm film camera (and thus a full-frame EOS digital SLR) has a focal length of 50mm and this approximates the perspective of a scene as seen by a human eye. This is the standard against which all lenses are compared. If the focal length is longer, the image will be magnified by a factor compared to 50mm. So, a 100mm lens will magnify the image 2x and the image will appear twice as close. You get the picture.
So the mm-denotation in the specifications of a telephoto lens (100mm, 200mm, 600mm etc.) does not refer to the diameter of the lens, but to the focal length, which only makes sense when compared to the 50mm focal length of a standard camera. Telephoto lenses can be either prime or zoom. Prime telephoto lenses have fixed focal lengths (like 100mm, 200mm), whereas zoom telephoto lenses have variable focal lengths (like 28-80mm). Canon divides all prime telephoto lenses (fixed focal lengths) into three categories: Telephoto lenses, standard and medium telephoto lenses and finally super telephoto lenses. Lenses with focal lengths of 135mm to 300mm, like the EF 135mm f/2.8 with Softfocus, EF 135mm f/2.8 with Softfocus and EF 300mm f/4L IS USM, are categorized as “Telephoto lenses”.