http://www.usa.canon.com/cusa/support/consumer/eos_slr_camera_systems/flashes/speedlite_420ex?pageKeyCode=writeReviewPage
Speedlite 420EX
7394
Features
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Maximum Guide Number 138 at 105mm setting; G.N. 101 at 35mm setting.
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Approximately 1/2-stop less powerful than 550EX.
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Full E-TTL flash operation with "Type-A" bodies.
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E-TTL features include high-speed FP sync mode, and FE Lock.
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Fully compatible with EOS-1v, EOS-3, Elan 7 series & D30.
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Powered by four AA-size batteries.
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Totally TTL-compatible with all "Type B" EOS cameras.