Pre-focusing and shutter locking on *istDS

I want to be able to pre-focus on a particular spot to await a moving object/person arriving at the spot, but I would like the shutter release button to be locked so as to be unable to be fired until the object is passing the through the focussed spot. I feel that there must be some camera setting that can achieve this but I cannot find any mention in the camera handbook. Does anyone know how to do this on the *istDS. ?

Keeping your finger on the button is the only way I know. I've pondered this too. Sre you thinking there should be a focus equivalent of exp lock button? would be handy.

You could try the following:

Use a manual focus lens, but set the camera on AF

Focus on the place you want.

Press and hold the shutter release - when something appears at the pre-focused spot the shutter should release.

I have adapted my old cable switch F for my istD this has a lock on it so extending John method of using a manuel focus lens. You can lock the shutter release on and even leave the camera and as long as the battery holds out and it will fire when something or someone comes into focus.
The adaption is quite easy following Matts instructions on using a 2.5mm phono plug.

David Benson

Thread is here: https://www.pentaxuser.com/forum/viewtopic.php?t=266
(on remote shutter release)
Matt

As far as I'm aware, this method (called trap focusing) is available on all Pentax SLRs with autofocus - certainly on all those that I've tried. I've found that it works best on relatively slow moving targets, although I suspect that the AF on my MZ-3 is perhaps not as good as it could be - you might have more luck wth faster subjects, as I would suggest that the more modern *ist(D/S) cameras have better AF.

This works with the *istD - I have a manual tamron lens, and have modified my Z1-P Cable release with lock position to fit the *istD.
metering has to be in manual and set beforehand, so there could be some considerable light change/ exposure level by the time the piccy is taken
Andy

Many thanks to all who replied and for the various suggestions. I have not yet had the time to try out what has been recommended, but will be doing so in the next few days.