Originally posted by lister6520 Note that the onboard flash will actually always contribute some light to the picture even in controller mode. In many situations though the contribution will be small enough to not be significant but there are cases when it can be a problem especially if you are shooting at short distance but have the external flash bouncing over a long distance.
Most of the control pulses that the on board flash uses to communicate commands to the external flash do occur when the shutter is still closed and do not affect the picture, however there is one last pulse that is flashed after the shutter is fully open, and it is the pulse which finally triggers the external flash. This happens even in controller mode, the difference being that instead of making a bright flash it makes one at about 1/50th power, which is enough for the remote flash to 'see' but normally low enough as not to significantly illuminate the photo.
I've discovered the same thing about the flash contributing a bit. I could never get my K5 to work right using the on-board as a control flash, but my K3 seems to work much, much better.
Besides the issue with macro, I've discovered that the DA 16-50 will be a problem when shooting at 16mm and a fairly close distance. It's not so much that the flash contributes much to the exposure, it's more a matter that the lens causes a flash shadow at 16mm, and you can still see it when the flash is set to control. It doesn't hit you over the head like it would if you were shooting with just the on-board flash, but it's there and distracting. I'm thinking about getting some radio triggers because I do a lot of macro and (now that I have the 16-50) wide angle interior stuff.