Just to add a little confusion, I have the da 300mm and the kenko 1.5x shq pz (non dg) and the focus goes back and forth so much I don't use it though the IQ is pretty good. I don't want to screw up the focus motor. the pentax 1.7x afa works great if you can find one, but they are pricey and you prefocus a bit to use it. I would try another kenko if I knew it would work, maybe mine is wonky. Too bad we can't switch to screw drive in the menu (if it would make any difference) I hope the new pentax TC doesn't take as long as the 60-250mm