Brief tests just firing off a few shots.
My Sigma 70-200 2.8 DG HSM operates correctly.
So does the Bigma 50-500.
My Metz AF2 would not fire though at any speed. Setting the Metz to HSS as mentioned by @pid solved that, so there's a temporary fix.
---------- Post added 05-05-16 at 06:47 PM ----------
Originally posted by G_Money When mounting a Sigma 12-24mm EX DG, camera will sometimes (but not always) ask to have focal length input, even though this lens doesn't require this for use with a K-3 or K-5. If I enter the default 100mm and then try to check it in the menu, the focal length item in the menu (camera 4) is greyed out, as it should be for a lens with the appropriate electrical contacts. Examining the EXIF data of an image shot at 12mm, the focal length appears as the correct 12mm. I realize that it's probably a Sigma firmware issue, but I'm surprised that it doesn't happen every time the camera is turned on with this lens mounted.
Try cleaning the contacts of the lenses. This happens to me on my workhorse lenses every couple/few months depending on use.
I'll clean the camera contacts at the same time of course, but the K1 shouldn't need that.