Quote Originally Posted by ic-racer View Post
Try this - if it doesn't work then the spring on the inside of the mirror box is broken (it's happened to one of mine).

Sorry to say it's a MASSIVE job and not worth doing, but you can file the stop down to adjust infinity focus (again what had to be done to mine).

Its a job I wouldn't tackle, and I used to fix then when I was a camera tech at Canon in the 90's!