Canon 600EXII-RT Instruction Manual page 37

m Bounce
When the bounce adapter is attached, or when the bounce adapter and
the wide panel are used together, underexposure may result since the
flash output decreases. Take necessary countermeasures such as
increasing ISO speed on the camera or applying flash exposure
compensation (p.28).
When Quick flash (p.21) is fired with the bounce adapter attached, taking
the picture after the flash-ready lamp is lit in red is recommended since
the flash output may not be sufficient.
The flash coverage is set automatically when the bounce adapter is
attached. You cannot change the setting. (When the <[> button is
pressed, <BOUNCE ADAPTER> is displayed.)
If you attach the bounce adapter to the flash when using an EOS
DIGITAL camera released up to 2004, set the white balance to <A>. If
you shoot with <Q>, appropriate white balance may not be obtained.
The flash light is further softened when the wide panel (p.39) is used
together with the bounce adapter.
If the subject is dark (underexposed) when you check the shot image,
perform the flash exposure compensation (p.28). You can also increase
the ISO speed when using a digital camera.
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