Pentax K-5 Operating Manual page 20

You can combine two or more external flashes (AF540FGZ, AF360FGZ or
AF200FG) or you can use two or more external flashes in combination with
the built-in flash. You can use the extension cord connection terminal on
the flash to connect the AF540FGZ. You can connect AF360FGZ or
AF200FG units as shown in the illustration below. Connect an external
flash and the Hot Shoe Adapter F (optional) to the Off-Camera Shoe
Adapter F (optional) and then connect another Off-Camera Shoe Adapter
F with external flash using the Extension Cord F5P (optional).
Refer to the manual of the flash for details.
When combining two or more external flashes
, Do not combine with accessories that have a different number of contacts,
such as a Hot Sh0e Gdpl asa malfunction may occur:
, Combining with flashes from other manufacturers may cause equipment
breakdown. We recommend using the AF540FGZ, AF360FGZ or AF200FG.
When Using multiple external flashes or Using an external flash with the built-in
flashi P-TTL is used for flash control.