Originally posted by Henrico
Shooting photographs with very narrow DOF's, like long tele's or a K1.2/50 can not be done super accurate through an OVF. That's not because you can't judge sharpness through the finder, you can, but because the finder is not precise enough neither is focus confirmation. The tolerances of in-camera dimensions are not precise enough. The only 100% reliable way to do it is using live view with magnification and IBIS off.
I agree with you that using Live View zoomed 100% is the best way to manually focus any lens on a Pentax DSLR that has LV. I use this method a lot when using manual focus glass, with the camera on a tripod.
Where this is not practical, say for moving subjects, remember that you can fine tune the AF confirmation green hexagon symbol (and beep) in the Auto Focus/Fine Adjustment menu. With a bit of practice using the AF confirmation adjustment together with establishing where it is best to focus your lens from (near or infinity), I find I can achieve almost as good as using LV