I bought a used EF 70-200 f2.8 II from KEH a couple of years ago. It was rated as EX (excellent) by KEH. It usually works perfectly for casual shooting or covering short events/sessions, but when I shoot sporting events, it loses the ability to focus after a few hours. I'm shooting outside typically in pretty warm weather (80 degrees F / 26 degrees C), and I'm not sure if that may have something to do with it.
I use a 7D mk II body with the lens, and am shooting roughly 2,000 frames per day; the problem begins after about 1,000 frames. I use back button focus.
Has anyone else ever had this or a similar problem, and if so, how did you solve it?
