On a digital camera, a diopter is a small dial or knob adjuster connected to the viewfinder. The diopter allows you to adjust the viewfinder sharpness to match your own eyesight. The diopter adjustment controls the focus of the viewfinder only, it does not change the focus of the camera lens.
DigiCam Help: Diopter Lens Wear eyeglasses? Want to shoot photos without them? Buy a digital camera with an adjustable diopter lens. Slight adjustments can improve clarity and sharpness when looking through the viewfinder.
Nikon Viewfinder Eyepiece Application Reference (PDF) 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.
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