This control enables near- or farsighted users to make dioptric adjustments to the eyepiece. Dioptric adjustment range is from -3 to +1 diopters.
To adjust, look through the viewfinder and turn the dial until the focus frame (not the picture) appears sharpest. In fact, this is easiest to do if you remove the lens first. If additional correction is needed, a Minolta Eyepiece Corrector 1000 can be attached to the camera's eyepiece.
The Minolta 9000's eyepiece shutter should be closed whenever you are taking photographs with the eyepiece not shielded by your head, as in remote-control photography, self-timer operation, or during long exposures. This will prevent stray light from entering through the eyepiece and affecting the exposure reading.