Mine would not allow me to change the diopter AND view finder was out of focus (for my eyes) once after a recharge of the battery. I cleaned the contacts, which seemed to have some light oil or preservative on them (battery and battery compartment) and recharged. Problem was resolved. That is what I based my guess upon. Nikon told me that if battery was low viewfinder would not function. I had thought this a mechanical not electrical viewfinder - so perhaps Nikon tech was incorrect.