There will be a 56mm f/1.4 later this year, which I expect will be very popular with portraitists. Capable of very shallow depth of field. With a field of view equivalent to an 84mm on full frame, it allows one to work closely for head-shots while maintaining a pleasant perspective. Available now is the 60mm f/2.4. I compared numbers of exposures, and found that I use it 40% of the time, with the 35mm used 34% and the 18mm 26%. It has close-focusing to 1:2 and a macro formula that is very flat field, producing minimal fall-off in the corners. Even at f/2.4, it is amazingly sharp and contrasty.
When I took delivery of the third lens, I went to a meeting in a classroom. Half the lights were turned off, for better projection, so I was shooting in very low light. After the meeting, we went for pizza so I shot in available darkness. I was testing the lenses, but also the X-Pro1 as a candid decisive-moment tool, trying to capture character and emotion. I included essential EXIF metadata.
AmiCUE on X-Pro1
I also had occasion to shoot a hockey game using the 60mm exclusively. I found the combination of OVF and lens to be ideal.
Hockey With the Fujifilm X-Pro1
So yes, I am very enthusiastic over this lens. I have also used it for nature and panoramas. It adds a very nice compressing on the z-axis for the latter. I am not obsessive over shallow depth of field, so really have no interest in the upcoming 56mm.
There are adapters for pretty much every lens in a focusing mount and I read a message from someone using an enlarging lens on a bellows. So any lens between 50mm and 90mm could certainly be adapted for this purpose. With the shorter focal lengths, one can work closers for more intimate portraits, with the long producing distance and formality. Of course, you lose auto-focus and aperture control for lenses that are controlled by the camera bodies. Some mounts attempt to address the later. Evidently, the difference between really cheap adapters and the most expensive is not of much significance. In any case, there are huge numbers from which to choose.
Metabones has announced development of a FX mount adapter with optics that will allow one to mount a lens and get the same field of view as if it were mounted on a full-frame camera. In so doing, you pick up an extra stop. Thus a 90mm f/2.8 keeps its field of view instead of that of a 135mm, but becomes an f/2.0! It only works with SLR lenses, Nikon and Canon initially.