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Canon EOS 40D Guide to Digital Photography by David D. Busch

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Speedlite 580EX II

This flagship of the Canon accessory flash line is the most powerful unit the company offers, with a GN of 190, and a manual/automatic zoom flash head that covers the full frame of lenses from 24mm wide angle to 105mm telephoto. (There’s a flip-down wide-angle diffuser that spreads the flash to cover a 14mm lens’s field of view, too.) All angle specifications given by Canon refer to full-frame sensors, but this flash unit automatically converts its field of view coverage to accommodate the crop factor of the EOS 40D and the other 1.6X crop Canon dSLRs. Compared to the 580 EX it replaces, the Mark II model recycles (inaudibly—no more hum!) 20 percent faster, and has improved dust-and water-resistance so you can use it in harsher ...

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