Yours regards, Alan Chan http://www.pbase.com/wlachan
P-TTL uses matrix metering, so in theory, it should give better results when center weighted metering could be fooled. And in case of *ist, it can give priority in the matrix metering area corresponding to the focal point. Off centered subjects is one example where P-TTL should be better.
Other reasons for P-TTL: multiple wireless TTL flash, high-speed sync TTL flash and flash exposure compensation.
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