Originally posted by FozzFoster AFAIK....
Medium format would have a crop of 0.79 (I think). So if you multiple full frame focal length by 1.5x to get APS-C, for medium format you'd multiple 0.79x...
Reading your question...
I think a 150mm medium format lens on an aps-c sensor would look like a 343.5mm
1.5+0.79 = 2.29x
150 x 2.29 = 343.5
I am very possibly wrong on this.
It's 0.79 for *digital* 645, yes.
A 150mm lens (assuming it covers the image circle of the 645Z) would "look like" a 120 mm lens when mounted on the 645Z, like a 150mm mounted on the K-1 and it would look like a 225 mm lens when mounted on the KP.
But this is all because we have grown used to relate everything to the 35mm (24x36, "Full Frame") format... If the standard were Digital-645, we would say that the K-1 has a crop factor of 1.3, and the KP has a crop factor of 1.9...