Pentax K-5 Operating Manual page 118

Set the camera to wireless flash mode when using an external flash in
combination with the built-in flash.
I
2
Press the four-way controller (•).
The [Flash Mode] screen appears.
Select w_ and press the
OK
button.
The camera is ready to take a picture.
The channel for the built-in flash is
displayed in the viewfinder and on the
LCD panel. The factory default setting is
CH1.
,When the drive mode is set to i3s(Remote Control (3s delaY)), MUP (Mirror
Lock:up) or M_P (Mirror Lock:up remote control) , or the lens aperture is not
w
set to the A Position; _-cannot be selected.
Changing the Built-in Flash Discharge Method
You can change the built-in flash discharge method used in wireless
mode.
Set in [21. Flash in Wireless Mode] of the [C Custom Setting 3] menu
(p.92).
1 On Discharges the built-in flash as a master. (default
setting)
2 Off Discharges the built-in flash as a control flash.
_m_ HS _ (High-speed f!ash sYnC)isn0t available With the built-in flashl