Originally posted by Spodeworld I understand that Pentax uses P-TTL which relies on a little pre-pulse from the flash. If you put a diffuser on the flash, does this impede with the camera's ability to set the flash level?
You are correct, the camera uses a preflash, but since the defuser will always be there there is not an impact in metering, because it uses the defused flash in teh metering as well.
the way P-TTL flash works, is that the camera meters the scene ambient light, and the impact that the pre flash has, both with open aperture. It then calculates the exposure required (i.e. flash duration) based upon what it reads back. All of this is done using the camera's standard metering and sensors