I just got a Pentax 100K and an adapter for medium format lens (6x7). The camera has a Shake Reduction feature that works great for the digital lens. When I put on one of the 6x7 lens, the camera asks me for the focal length of the lens I'm putting on. It would be easy enough but medium format lens are a different scale than 35mm lens. Should I use the 6x7 scale or the conversion to 35mm scale? Does anyone know that conversion?