Trailing curtain sync on K3 Mkiii with Pentax AF540FGZii

When ‘flash on’ is selected on camera and ‘trailing curtain sync’ on flash, the flash fires twice, first after the leading curtain opens, then just before 2nd curtain closes. Annoyingly both contribute to the slow shutter speed exposure. Has anybody found a way of just getting one flash on 2nd curtain, other than the clunky method of sticking your hand over the first flash. I get that Pentax has reduced flash modes on the camera, leaving the photographer to select settings on the flash, though not sure why the range of modes is increased for some exposure modes, which doesn’t include ‘manual’ which is the one I would choose for slow shutter speed photography. Similarly I can’t select trailing curtain sync on the flashgun when it is in manual mode?? In summary, how do I do correct trailing curtain sync photography with a K3iii and the AF540 FGZii flash?

I dont use trailing shutter sync often, but seem to remember it is a P-TTL only mode on the Pentax flashes. I would need to find the manual to check.

As far as two flashes, I think you are mistaking the pre-flash for the first one. It wont contribute to your exposure as it takes place while the mirror is down.

Thank you Pschlute. This is helpful. I checked the manual again and I can find no reference to trailing curtain sync being a PTTL only function in the sync mode section, which, reasonably enough, was the only bit I read for my particular project. However, this does match the reality of the situation and when I read the flash mode section, there is a table of functions available for each mode, which shows that trailing curtain sync only has a tick in PTTL mode. (Clearly, I must read and memorise manuals more comprehensively - Oh Joy!!)

I scoured the Pentax forums before posing my question to see if my problem had arisen before and there is one about the first flash being a pre-flash that has no impact on the picture being taken, I did some little tests in the house which showed that the first flash does in fact expose the scene, as well as the second. This might still be my problem and I probably need to read even more of the manual and to practise more ‘in the field’. Thanks again for taking the trouble to provide me with a very helpful response.

Just a thought....you are not turning the LED beam on are you ?

The trailing curtain option is only a P-TTL mode so not available when the flash is set to Manual output.

What exposure mode are you using on the camera itself ..... Manual ? If so what shutter speed are you selecting.

Also what lens ?

This won't include the K3III, but might help?

https://www.pentaxuser.com/article/complete-pentax-flash-guide-946

Looks, unfortunately, that Nigel is no longer active on this site. Or PF for that matter.

Thanks Peter,
I had the Flash on P-TTL as I had selected trailing curtain sync. I was literally trying everything until I got it, before I know it had to be P-TTL. My camera was on manual, 2.5 secs, f2.8, ISO 400. The lens was the Pentax 16-50 DA* I thought that there were perhaps settings on the camera I had to select to get successful tcs. but I now realise this is not the case. In casting around the menu I found there were more flash options for some exposure modes, which puzzled me. I now don't think, however, that this is relevant to my issue.
Thanks again, John

Thank you for this John. I have downloaded the guides and they look well worth reading. I shall learn much. John

Ok.. Can you post some images which show the overexposure. That may help.