The onboard flash of most DSLR are not that effective beyond a couple of meters and for whatever reason, several DSLRs from different manufacturers I'm aware of use a strobing of the onboard flash for focus assist, rather than adding an additional focus assist lamp. Most people who do a lot of flash photography, purchase a dedicated flash like the FL-36 or FL -58 or the Metz 48 and 58, all of which are fully TTL compatible. These flashes also come with a red focus assist light and have a higher effective range.
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Dave
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Olympus E-510
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