[clackers]

Thanks, clackers, for actually addressing me, and my problem. I seem to have mislaid the cable, but shall get another. I am thinking that if the Pentax dedicated works on the camera at any shutter speed, then the hot shoe cable is just an extension of the flash, so that's why it would have worked at the wedding.
Cheers, Trish

That's right.

I use one that's not particularly long with a metal bracket, but I have also held my hand containing the flash out to the side and up, uncoiling it.

[beholder3]

Ok, that's cool it only needs one flash as a slave. I venture to think that flash has to be Pttl Hss compatible in slave mode such as your 540. I know my af540fgz's are but my sigma 610 super isn't. It will only perform pttl Hss as a controller not as a slave.

I have no Sigma 610 super, but since that flash can do HSS on camera as far as I know it would probably work as well on the acons, simply because their concept does not require something to be "slave" or "master" in any setting, since that is a concept only applicable for multi flash setups.
If the flash standalone works on the camera with HSS then it should work on the acons as well, just as with any PTTL cable.

[mcgregni]

The Pentax accessory flashes, (AF-540FGZ I or II), plus probably some of the higher specced third party options, allow the on-camera trigger flash to function as either a 'master' (adds it's light to the scene) or ' controller' (does not ) . So you have the flexibility as needed to either restrict the effects to your slave unit, or include some effect from the camera position ....

In my opinion, there are plenty of good ways to use an on-camera light in conjunction with a slave, most obviously as front fill for HSS portraits, so in fact my on-camera trigger flash is usually set to 'master' for my HSS work. Makes it seem less like a waste a money. ...... !