I am new to this forum, and I realize there has most likely been tons of discussion about soft focus with the Canon 100-400 lens. I use this lens on a 7D, and it is excellent at all focal lengths- good sharp images on fairly close subjects. My problem is at 400 at a distance. Recently I ran some tests with a friend- he has the same setup, so we put his and mine on tripods, all settings the same, and took the same shot. His was most definitely sharper. I put his lens on my camera and found it was still much sharper than my lens. The one thing I neglected to do was put my lens on his camera. I called Canon and was told to send it and the camera in for calibration. I am worried that since it is really great on close subjects, calibration may mess this up. Is it calibration, or is it some other problem? Both of our lenses are refurbished, bought directly from Canon. And no, my friend was very careful to pay attention to me so I wouldn't switch lenses! Any help is very much appreciated.