Canon Speedlite 600EX-RT - Manual (Page 101)

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C: Setting Custom Functions
C.Fn-12: 3 (Flash recycle with external power)
0: 1 (External & internal power)
Charges in parallel using both internal power and external power.
1: 2 (External power only)
Internal power is needed to control the Speedlite. By using only external
power for charging, you can minimize the depletion of the internal power.
C.Fn-13: 6 (Flash exposure metering setting)
0: 4 (Speedlite button and dial)
1: 5 (Speedlite dial only)
You can perform flash exposure compensation by directly turning <9>,
without pressing the <@> button.
C.Fn-20: 7 (Beep)
You can enable a beep to sound when the Speedlite is fully charged, or
when a slave unit is fully charged during radio wireless transmission flash
shooting.
Note that when set to 1, a beep will sound as a warning when the flash
firing restriction is activated due to a temperature increase in the flash
head.
0: OFF (Disabled)
1: ON (Enabled)
COP
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