I have had two M42 screw mount Super-Takumars (55mm F1.8 and 135mm F3.5) for a few weeks now. I almost immediately felt home with 55mm Super-Takumar but my initial feels with 135mm one were quite mixed ones. It felt too long for manual focusing with X-Pro1 which do not have any kind of focus peaking to help focusing. I usually use 3x focus magnification to check the proper focus (10x magnification is way too wobbly). Fortunately, i am usually able to get nice focus straight in without using any focus magnification. Now that I have little bit more experience with the 135mm I think it is usable with X-Pro1 but you have to accept increased amount of non-keepers as compared shorter focal length manual focus lenses. I can use it even wide open (f/3.5) indoors in quite dim light and get at least some good and reasonably sharp shots. Not bad. Outdoors it works very nicely with apertures 8-11 or so (of course wide open is nice for bokeh and blur too).