Originally posted by Canada_Rockies I think the poster intends to not use the on board flash at all by using a cable rather than wireless mode. With the cable, he can use P-TTL without enabling the on board flash. It makes perfect sense to me.
There may be some confusion in terms here. To me, a Pentax 540 would be an onboard flash when it's mounted in the hot shoe. A 540 is not onboard when it's used remotely, whether by wire or wirelessly. The pop-up is not an onboard flash, it is an inboard flash.
Anyway, that doesn't directly relate to my point. My Sigma 530 Super takes four seconds to recharge, about as long as a Pentax 540 and twice as long as the built-in on my K20, so I don't see where the pop-up flash is causing a delay.