Can I suggest you check that the screen is seated correctly. They are interchangeable and can be put back in the wrong position. Also if you remove the screen, check the mirror, this may also have been removed at some time and not put back in the right position. is the pressure plate on the back of the camera in the correct place. too? If the image shows 'in focus' when you are taking the picture and on the results on film it are not then these ares practically the only things that can be out of position.
I doubt very much if the lens has anything to do with it.