Canon Telephoto Zoom Lenses

Telephoto lenses include two broad categories: Telephoto lenses with fixed focal lengths (also called prime lenses) and telephoto lenses with variable focal lengths, called zoom lenses. All telephoto lenses make the subject appear closer than it really is when viewed with the naked eye and the amount of magnification is determined by the difference between the focal length of the telephoto lens and a normal lens of which the focal length is 50mm (A lens with 50mm focal length is regarded as approximating the view with the naked human eye the closest). So a telephoto lens of, say, 600mm, will magnify a subject 12x or let it appear 12x closer.

In the case of telephoto lenses with fixed focal lengths (prime lenses), this never changes. If you want to take a picture of an eagle way up in the sky and your 100mm telephoto lens is still not powerful enough to bring it close enough to recognize, you’re stuck. You either need a more powerful prime telephoto lens or a telephoto zoom lens. A telephoto zoom lens has variable focal lengths, usually starting at 70mm at the low end. The EF 75-300mm f/4-5.6 III has an annotation 75-300mm in its specifications and this means that its focal length can be adjusted to from anything between 75mm to 300mm. So it can magnify by anything from 1.5x to 6x. You focus on the eagle in the sky and then simply turn the focus dial magnifying the bird as many times as you like, within the limitations of the lens.

Examples of Canon telephoto zoom lenses include the following: EF 75-300mm f/4-5.6 III, EF 70-300mm f/4-5.6 IS USM, EF 70-200mm f/2.8L IS II USM, EF 70-200mm f/2.8L USM and the EF 28-300mm f/3.5-5.6L IS USM. The last one is a very complex zoom lens, with as many as 22 optical elements. The interesting feature is the fact that its low end focal length is 28mm, which is less than the 50mm, which is regarded as standard. This means that this lens will provide you with a wide angle view at the low end setting of 28mm focal length in addition to the telephoto view (magnification) at the high end of the setting.