Sony HVL-F45RM Operating Instructions Manual page 46

Flash distribution setting
You can press the MENU button and select [FLASH DISTRIBUT.] to
specify the flash distribution pattern. (The flash distribution setting is
applied to the flash coverage whether it is selected automatically or
manually.)
STD : Flash coverage with standard flash distribution
CENTER : Flash coverage with priority given to guide numbers
EVEN : Flash coverage with priority given to wider periphery
Notes
Depending on the focal length specified for photography, the periphery of the
screen may appear darker. In such case, change the flash distribution pattern.
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