Originally posted by totsmuyco I've tried setting the flash on PTTL and use manual mode. The results were not good.
What wasn't good about the results?
Did you do your part with respect to controlling the ambient exposure through the manual camera controls?
The green button can be very helpful in this regards (e.g., select ISO and an aperture and let the camera decide on the shutter speed).
I'm asking because having the camera in "M" mode and the flash in P-TTL mode is the recommended approach. Otherwise, you'll have the camera assume what you are trying to achieve and hence get the slow shutter speed scenario you mentioned, etc.
AFAIC, you have the most control and achieve the best possible consistency when using the camera in "M" mode and use manual power control with the flash. However, letting the flash determine its power level on its own (in conjunction with the camera), should give you usable results. You should expect to use flash exposure compensation (on the flash or in the camera menu), though, to season the flash output to taste.
P-TTL is an ancient flash system that is in dire need of an upgrade to become a fully useful automatic exposure support system (in particular when multiple flashes are involved) and you cannot expect it to produce a good result in all situations.
Depending on the camera you use (e.g., K-5 (II)), you'll have to deal with some P-TTL bugs/shortcomings that will guarantee that flash exposure will be off in particular situations. Try whether you see any difference between bounce versus non-bounce scenarios and also make sure you don't exceed the power range of the flash. If you are too close to a subject, the flash may not be able to further reduce its power. If the flash is maxed out, you'll get underexposure in certain situations (subject too far away or bounce distance too large). It's one of the disadvantages of P-TTL that you don't see whether the flash is operating at its limit.