Originally posted by ivanvernon I have wondered why SR cannot be built right into the medium format cameras just as with the K mount cameras. It is such a desirable feature that I have to imagine there is some major reason why not. I have no idea whether there are either engineering or economic barriers to doing so. Maybe Adam can opine on this.
There are some non-obvious factors involved due to lens magnification. The effect of the lens on the image at the focal plane is a transformation of angle to displacement. When the photographer moves the angle of the camera-lens assembly, a point in the image moves on the focal plane. How much it moves depends on the magnification and, in the case of roll, on the distance from the optical axis of the correction servos. Hence, correcting the focal plane by moving it requires measuring the angular motion (rate sensor integration is probably good enough for this) and then calculating focal plane motion to correct it. At the other end of the optics, angular motion can be corrected 1:1 if performed ahead of the lens objective (or 1:2 if certain configurations of mirror stabilization systems are involved).
Nonetheless, building MS into the camera body allows motion to be corrected independently of the lenses, so long as focal length is known. This requires less material, complexity, and cost than making every lens MS. However, the Z, D, N, etc. do not already have MS in the body, so we have to live with whatever is available. To MS the huge number of FA lenses used with the present Pentax MF camera bodies calls for an external stabilizer, or a much lower cost but inconvenient in some cases tripod.
What might be possible, if camera space exists, would be for an affordable upgrade to the 645Z. I suspect that it could only be affordable if a relatively large fraction of the 645Z ownership population were on-board with the idea.