Originally posted by Pentigor I'd like to couple the k-70 with some kind of 18-50lens with aperture ring and auto-focus (DC) for my video needs
I don't think there is any such lens. All the Pentax lenses with silent AF have no aperture ring. Maybe there is some third party lens that fits. I can't think of one off the top of my head.
Honestly, for video, I would recommend something like Samyang cine lenses. High quality primes of various focal lengths, manual focus, click-less aperture ring, T-stops, follow focus geared focus ring texture..
Keep in mind that aperture can still be changed. Lenses without aperture ring still can change apertures, but it is done through the camera, not by hand on the lens barrel. Main reason to use an aperture ring is when you are using adapters or reversing a lens for macro work. For most other needs, you don't need a physical aperture ring on the lens.