"Optional Nikon eyepiece 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 ofSLR 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. . Each Nikon eyepiece diopter incorporates a numerical value, represented by a minus value (nearsighted) or a plus value (farsighted) number, enabling you to select the appropriate diopter for your vision and your camera model. . The eyepiece's diopter value is, when combined with the viewfinder's minus one value, the end-result value. No combination of the camera's base value of minus one and a given accessory diopter's value is required to arriv|Compatible with D3000, D300S, D3100, D5000, D5100, D7000, D90"