Pentax K-5 Operating Manual page 18

Wireless Flash Control (P-TTL Flash Mode)
When using external flash units (AF540FGZ or AF360FGZ) for
wireless shooting, the following information is exchanged between
the flash units before the flash is discharged.
Press the shutter release button fully.
4,
1 The flash directly connected to the camera emits a control flash
(relays the flash mode of the camera).
2 The wireless remote flash emits a test flash (relays confirmation
of subject).
3 The flash directly connected to the camera emits a control flash
(relays flash output to the wireless remote flash).
* The flash directly connected to the camera wilt emit a control flash
one more time after this to relay the flash duration time when HS _.
(High-speed flash sync)is set.
4 The wireless remote flash discharges.
%
When the wireless mode of the external flash directly connected to the
camera is set to [MASTER] or [21. Flash in Wireless Mode] (p ! 91 ) s set
to [On] fo r the bui!t-in flash i all the flashes wi!! discharge simultaneously .
Red-Eye Reduction
As with the built-in flash, the red-eye reduction function is available
with an external flash. However, this function may not be available on
some flashes or may have restrictions for usage conditions. Refer to
the chart on p. 187.
;Th e red-eye reduction function Works by disCharging the flash twice
even when on!y an externa! flash is used. (p.80)
If the red-eye [educti0n function of the built-!n flash is used when the
externa! f!ash is set as the s!ave unit or with the wireless functioni the
pre-f!ash for red-ey e reducti0n wil! trigger the externa! f!ash Do not use
the red-eye reduction function when using a slave unit _