Today I used my 300mm Nikon lens on my X-t1 to try out manual focus with this kind of lens. The X-t1 has this focus aid that shows you a small zoomed in part of the screen besides the main screen and this works great. All the pictures are taken hand held with a shutter time of 500. The pictures of the flower give a nice mood and because of the aperture of f4 only a small sliver is sharp. The picture of Darth, our cat, shows a good sharpness in the eyes and the bridge is sharp to, at least part of it because the aperture was also f4. The butterfly was more difficult to get sharp but that was because of the wind, I shot a burst of pictures and prayed for the best, something a normally never do. Overall manual focusing works fine with this kind of lens.When I use this lens, made between 1987 and 2000, on my Nikon D7100 you can use the autofocus but it is slow, there is no motor in the lens like you have with modern lenses, it’s all mechanical and you notice, and hear it. As long as the subject is not moving to mush and you are not in a hurry it works great. .