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Canon® EOS Rebel XSi/450D Guide to Digital SLR Photography by David D. Busch

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Telephoto Extenders

Telephoto extenders (often called teleconverters outside the Canon world), multiply the actual focal length of your lens, giving you a longer telephoto for much less than the price of a lens with that actual focal length. These extenders fit between the lens and your camera and contain optical elements that magnify the image produced by the lens. Available in 1.4X and 2.0X configurations from Canon, an extender transforms, say, a 200mm lens into a 280mm or 400mm optic, respectively. Given the XSi’s crop factor, your 200mm lens now has the same field of view as a 448mm or 640mm lens on a full-frame camera. At around $300 each, they’re quite a bargain, aren’t they?

Actually, there are some downsides. While extenders retain ...

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