Originally posted by tabl10s I'm not sure what protocol is used if I have one as the master and the other a slave.
If you aren't using P-TTL, then your flashes have to be operated in manual mode, so setting them to be a master or slave doesn't do anything. With radio triggers you set a radio connected to the camera to be a transmitter and the other radios to be receivers, but the flashes connected to the triggers just know they are supposed to fire, no other settings are communicated. Wireless communication with P-TTL is done with light pulses from a flash directly connected to your camera, but it doesn't have to be the built-in flash. You can mount one of your Metz' to the hot shoe on the camera and set it to be master or controller and any flashes you want triggered wirelessly using P-TTL have to be set to be slaves. Or set the built-in flash to be controller, don't have any external flashes directly connected to the camera and set the external flashes to be slaves. And don't forget to pop up the built-in flash.
Just to make it more confusing, both the camera manual and the Metz manual I have refer to Pentax's hot shoe adapters and extension cord, but the camera manual says you can set an external Pentax flash connected this way to be the master flash, even with contrast sync, and the Metz manual says that if you connect an external flash this way, it has to be set to contrast control and the built-in flash still contributes. The Pentax Hot Shoe Adapter F has a low enough profile that you can use an extension cord with it
and pop up the built-in flash, so perhaps that is the only way to use a Metz flash with contrast control, but it would have to be set to be a slave.
Or you could give up trying to understand how P-TTL works with external flash and set your Metz' to be Servo slaves. In this mode, simple flashes of light from any other flash will trigger the Metz to fire, although there are settings to compensate for premature triggering because the camera is pre-flashing to eliminate red-eye. This mode could be a problem at weddings and school concerts where more than one person is doing flash photography.
Personally, I think P-TTL gets a bad rap because you have to rely on the camera's programming, instead of controlling every variable yourself. However, if you are just trying to get reasonably well-lit pictures without special effects, it is more convenient and is somewhat predictable. In general, I think flash photography is more challenging because you need a good eye for the effects of flash without actually having the true lighting conditions visible to you when you compose the shot. And that applies no matter what protocol or triggering method you use.