My list of 645D lenses contains the 35mm A, FA; 75mm, 120mm A, FA; 150mm, 300mm/4; 600mm A; 150-300mm. These are all excellent, at least the versions I have. There are some P67 lenses that are also fairly good, including the 100mm macro, the 800mm ED, and the 45mm with a Zoerk shift adapter. The 45mm isn't too bad and perhaps the best shift option when stopped down to f/11.
Alternatively, you can use the Arsat/Superrotator 45mm in its various incarnations and levels of image quality, some almost on par with the P67 45mm when stopped down. There is an incredible number of Russian and East German lenses available via adapter, including the 35mm Zodiak Fisheye (quality varies, some are not too bad), the 150mm Kaleinar and the 250mm Jupiter as fast Telephoto lenses, and the rare 500mm APO Arsat. All of these are nice and fast, but have less contrast than the Pentax lenses, less sharpness and some aberrations.
Also in P6 mount and adaptable are the Carl Zeiss Jena lenses, including the 50mm Flektogon and the 180mm and 300mm Sonnars. Of these, the 180mm Olympia Sonnar is wonderful with narrow depth of field and great bokeh. Then there is Carl Zeiss Jena's 1000mm/f5.6 mirror lens, certainly a brute, but perfect for the digital sensor because of its lack of chromatic aberations. For a few years, Schneider produced a very fine set of lenses for the late Exakta 66, including the 60mm Curtagon as well as the 150mm and the 250mm Tele-Xenars. These are exquisite and on the same level as their Rolleiflex counterparts.
Adaptations might also compensate for the only major shortcoming in the Pentax line-up, the lack of high speed lenses in the portrait range, when compared to the 110mm/f2 Zeiss Planar for the Rollei or the 100mm/2.2 for the Hasselblad. One of the fastest lenses in this range is the 12.5cm/f2 Schneider Goettingen Xenon of war-time glory, which gives highly unique portraits. I use it in a dedicated Burke and James, Chicago, mount. A less unusual alternative is the 12.5cm/f2.5 Leitz Hektor for the Visoflex. This lens is actually fairly sharp, except at its widest aperture, where it has a nice glow in the highlights. The Hektor comes with a focusing mount that matches nicely with the many P645/M39 adapters available on the internet. Most of the Visoflex lenses cover medium format, and the Hektor is no exception.
You can adapt others, such as the legendary Kinoptik movie lenses, and I have good experiences with the 210mm. Other truly great lenses for the 645D are the Mamiya APO telephoto lenses for the RB and RZ 67. These can be adapted with a helicoid. They are a bit heavy as they have their own shutter built in, but the results are excellent.
Finally, you can adapt countless macro and soft focus lenses, either by using the M39 adapter available on the internet or simply mounting your soft focus lens into some extendable tubing. In a previous post I have shown images of magnolia blossoms photographed with adapted soft focus lenses on the P645D.
Lens adaptations is where the 645D shines. Your choice of lenses is limitless.
