Flash External Metering - Canon Speedlite 600EX-RT Instruction Manual

//.: Flash External Metering

The Speedlite's built-in external metering sensor measures the flash
reflected from the subject in real time, and stops the flash when the
standard exposure is reached.
"Auto external flash metering" can be used with the EOS digital
cameras released since 2007. "Manual external flash metering" can be
used with all EOS cameras.
/: Auto External Flash Metering
This enables you to perform automatic flash shooting. The flash output
is automatically adjusted according to the ISO speed and aperture set
in the camera.
Flash exposure compensation (p.22) and FEB (p.23) are available during
auto external flash metering.
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Set the flash mode to </>.
Press the <E> button and set to
</>.
If </> is not displayed, set the
flash Custom Function to C.Fn-05-2
(p.96).
When you press the camera's shutter
button halfway, the effective flash
range is displayed.