Correction lens, 0.0 neutral. An easy-to-use viewing and focusing aid which allows near and farsighted photographers to view the finder image accurately without wearing eyeglasses. Optional Nikon eye espandi...piece diopters allow you to optimize your SLR viewfinder’s sharpness in conjunction with your individual eyesight. Eyepiece diopters are designed for specific camera models and are identified by a plus, a minus or a neutral numeric diopter value. Standard eyepieces supplied with Nikon SLR cameras have no corrective value and are for dust protection only. Select eyepieces are supplied with a rubber coating designed to lessen scratching of a photographer’s eyeglasses. Nikon SLR cameras (without built-in adjustable eyepiece correction) have a base diopter value of minus one. This is why you won’t find an accessory Nikon eyepiece diopter valued at minus one. Minus one is considered the optimum starting point for the majority of SLR users with normal vision. The combination of the camera’s viewfinder components and a clear (standard) eyepiece form a virtual image of a subject on the camera’s focusing screen that is the approximate equivalent of a viewing distance of one meter.