Some grain focusers have to be focused. The one I have has an outlined rectangle and an adjustable eyepiece. I make sure that is sharp before using it (I believe you did that but check before each use). Have the focuser on a piece of the same weight paper you will be printing on in the easel. Unlike Rudolf, I focus wide open and then stop down assuming that if it is focused wide open it will be that much better stopped down but everyone has their own technique. I don't look through my reading glasses when using the grain focuser.

http://www.jeffreyglasser.com/