Originally posted by chiefsilverback K5ii is set to full manual with flash in 'wireless' mode and the menu option to command only (not assisting with the exposure). Does the in-built flash still pre-flash even in this scenario?
Yes. Command means it is going to communicate with the remote flash optically using the P-TTL protocol. The camera fires a pre-flash to measure exposure, then sends the info to the remote, then triggers everything. Sorry, but there is no way to do what you want to do with the k-5II. The k-3 does have a full manual flash setting and it will work as you want. The only way to do what you are trying to do on the k-5II is with radio triggers like the Cactus v5.
Originally posted by chiefsilverback I've had the shutter as slow as 1/10!
That's fine. Anything UP TO 1/180 will work, but the camera will not fire the flash at all if you set a speed FASTER than 1/180th.
You might want to read through mcgregni's guide in post #6.
---------- Post added 02-15-16 at 01:03 PM ----------
You might also want to read up on manual flash and balancing ambient light with flash. I often shoot at 1/10th second with flash to balance the ambient. But the flash is going to come and go very quickly, far quicker than 1/10th. It might be 1/2000th at full power and 1/20,000th at low power, each flash will be different and I do not know the numbers for the 540, mcgegni's guide might have those. So you can use the flash to illuminate the subject and the slow shutter speed to illuminate the background. But you have to then calculate two different exposures. One for the flash and subject and another for the ambient and the background.