Triggering Studio Flash Remotely from Hotshoe Trigger

Apologies for this novice question. I have a Pentax *ist D which came with no manual. I want to trigger some lighting with a hotshoe trigger. It works in Auto, but when I go to Shutter Priority, it doesn't trigger. How can I get it to trigger in Shutter Priority?

Thanks for help!

Re the manual, you should be able to find something here.

Probably you're using a too fast shutter speed, when you go faster then 1/180 it stops triggering the hot shoe so the trigger you've on it.
YOu will notice you can't get 1/180 in manual or any other mode so 1/160 is the fastest you can get or you need to use x-sync, it's the X on the mode dial, it will set the shutter speed on 1/180 but you can't move it off from it.

The shutter speed has to be no faster than the "flash synch" speed, or 1/180 second for Pentax cameras.

The easiest thing is to set the shutter speed in manual and then set the aperture according to the flash output. You can use a flash meter, but if you start at f8 and then see what happens, you can lighten pictures by opening upo (f5.6..f4...etc.) or darken pictures by closing down (f11...f16...etc.)

With shutter priority the camera will want to adjust the aperture according to the ambient light, which isn't suitable for using studio flash.

Hope that helps!

Note that for the istD, top sync speed is a mere 1/150 sec.

Thank you for the correcting