The S-M-C Takumar 6X7 105mm f/2.4 lens in its three different yet optically identical incarnations is probably the most recommended lens for both the Pentax 6×7 and the Pentax 645 series of medium format cameras. I never really understood this, the SMC Pentax 67 90mm f/2.8 lens that I already owned is on paper not that different if you only consider the aperture and focal length. Yet the 105mm at open aperture has an amazing and quite a unique bokeh which makes it great for portrait photography out in the field.
I’ve only tried out the lens on my Pentax 67II so far and I’m keen to use this lens on my Pentax 645NII via the affordable Fotodiox adapter I picked up earlier. I love all my other Takumar lenses, if it works out as well on my Pentax 645NII, this lens will be a keeper!