Pentax appears to be hard at work on a medium format digital camera based on a recent patent application filing. (See US Patent Application No. 20080232791) Above, you see “Figure 10″ in the patent application.  Below, is Pentax’s description of Figure 10.

FIG. 10 shows the finder optical system of an SLR camera having the relay finder optical system according to the present invention.

[0038]This SLR camera is provided with a photographing optical system 10, a main mirror 11 supported by a mirror box 14, a relay finder optical system 20, a Lupe (magnifying) optical system 30, and an imaging back 52 having an imaging device 51 installed behind the mirror box 14.

The patent is specific to a relay finder optical system rather than an entire camera:

The present invention provides a relay finder optical system of an SLR camera, in which aberrations can be well corrected and further miniaturization can be achieved, while securing a necessary eye relief, an apparent visual angle, and a finder magnification.

While the patent does not cover the camera system as a whole, it’s interesting to see Pentax’s developments, which have been rumored for some time now.