Although the combined viewfinder/rangefinder of the Leica M even helps photographers with minor eyesight deficiencies to focus precisely, optimum eye-to-camera matching is the best alternative. The M system correction lenses provide this, and they also make composing images in the viewfinder more comfortable than it can be with eyeglasses. These lenses are available in grades of plus/minus 0.5, 1, 1.5, 2 and 3 diopters. Prior to ordering, it should be noted that the Leica M's viewfinder is preset by default to -0.5 diopters. So anyone wearing glasses of 1 diopter strength would require a +1.5 diopters M system correction lens.