The Leica Correction Lens M -1.5 provides a diopter adjustment, making composing images in the viewfinder more precise and comfortable. The correction lenses are available in +/- 0.5, 1.0, 1.5, 2.0 and 3.0 diopters. Please note that the Leica M viewfinder is preset by default to -0.5 diopters. If the diopter strength of your glasses or lenses is -2.0, this correction lens fits your eye!