Ok, I'm going to describe my 'understanding' and please correct me and fill in the gaps if you will....
So TTL means 'Through the Lens' so the metering that controls the camera flash is more accurate. P-TTL is a more advanced version of this... (big gap here).
When I have my flash set to P-TTL and active as an off camera slave it is 'controlled' by my on camera flash which triggers it by 'flashing' before the shot...
Now in camera, the metering of a shot in a dim room is usually indicating that the shot is very underexposed. Because it actually 'meters' at the time of the shot... So if I press the green button to set exposure settings in manual mode, it is NOT taking the the flash into account at this time....
And if I do this, and then shoot I will likely end up with a much slower shutter speed then necessary... But the shutter speed does not matter with flash... because the flash is sooo fast that the exposure will really only catch the moment of the flash... (ANOTHER big big gap...)
Or will the camera compensate for the flash and adjust the shutter speed at the time of the shot after doing it's P-TTL thing??
Help please...
Ken