I just received an EX grade Canon F-1N from KEH and it does not focus to infinity. I have reseated the focusing screen (PE, split-image/microprism) and the problem persists. For example, when my 24mm f/2 is set to infinity, it focuses at about 10 feet. With my 50mm f/1.4 the problem isn't as bad, but it, too, is not reaching infinity. Both lenses work fine on my A-1. Any ideas? I hate to return it but will if I need to. A bit frustrated with KEH recently - I had to send two copies of the 35-105 f/3.5 back because of different problems.