Canon MT-26EX-RT Macro Twin Lite - Manual (Page 105)

105
> :Setting Personal Functions
P.Fn-05: + (Quick flash)
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.