Correction lens, –3.0 strength, for Nikon D-SLRs that feature a circular-eyepiece. 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. Each Nikon eyepiece diopter incorporates a numerical value, represented by a minus value (near-sighted) 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 arrive at the final desired value. In other words, if you require a diopter of plus 3, simply add a plus 3 diopter to your camera.