Canon Macro ring lite MR-14EX II Instruction Manual page 53

Shooting with firing group C pointed directly toward the main subject may
result in overexposure.
On the models listed below, wireless multiple flash shooting adding slave
C is not available when the <a> mode is set (with C.Fn-15-0). When
the <q> mode is set, wireless multiple flash shooting can be performed
on all type-A cameras (p.2).
EOS Elan II/Elan II E/50/50E, EOS REBEL XS N/REBEL G II/3000N/
66, EOS REBEL 2000/300, EOS REBEL G/500N, EOS IX, EOS IX Lite/
IX 7
If there is a fluorescent light or computer monitor near a slave unit, the
presence of the light source may cause the slave unit to malfunction and
fire inadvertently.
If you shoot or fire the test flash with slave A and B positioned when
C.Fn-15-0 is set, slave A and B may fire. Turn off the slave A and B.
You can fire the modeling flash even during wireless multiple flash
shooting (p.23).
If the slave unit's auto power off takes effect, press the master unit's test
flash button to turn on the slave unit. Note that the test flash cannot be
fired when the camera's 3/1/4/7/2 timer is operating.
a: Multiple Flash Shooting with Slave C Added
51