Canon Macro Twin Light MT-26EX-RT Instruction Manual page 105

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P.Fn-05:
You can set whether or not to fire the flash (fire the Quick flash) when
the flash-ready lamp is lit in green (before the flash is fully charged) to
shorten the charge waiting time.
0: ON (Enabled)
1: OFF (Disabled)
When Quick flash (p.27) is fired during continuous shooting, underexposure
may occur since the flash output decreases.
(Quick flash)
>:Setting Personal Functions
105