Dear Phil:
Regarding the rough spots that you experienced when turning the focusing ring on you 21-35mm zoom R lens, have you had anymore problems like that lately? If not, then it's probably all right. When you did experience this roughness when turning the focusing ring, do you recall if the lens was mounted on a body, or were you just holding the lens by itself? Rotating the focusing ring with the rear lens cap on actually causes a vacuum effect within the lens while turning it, which sometimes makes the focusing ring a bit more difficult to turn, due to the internal vacuum effect generated. Try rotating the focusing ring with the rear lens cap off, and the lens not mounted to a body, and you will probably find that the focusing ring turns a bit easier. Moreover, when you store your lens, make certain that you don't always store your lens in the same position all of the time. An easy way to go about this is to store your lens upright during the even number months, and then store your lens upside down during the odd number months. If you store the lens on the same side all of the time, the grease on the threads inside the lens will accumulate all on one side do to gravity, and then the focusing ring may start to become harder to turn, especially in the cold climates.
Regards,
Dale
