Canon Macro Twin Light MT-26EX-RT Instruction Manual page 31

a: Fully Automatic Flash Photography
If the flash exposure confirmation lamp does not light or if the subject is
dark (underexposed) when you check the shot image, move closer to the
subject and shoot again. You can also increase the ISO speed when
using a digital camera.
"Fully automatic" refers to <A>, <1>, and <C> shooting modes.
Even when attached to a camera that supports the E-TTL II autoflash
system, <a> is displayed on the LCD panel.
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