There is no ZM 45mm F2 lens. Some have taken the Contax version and refit it to Leica M mount though, and obviously there is no difference in quality. Among ZM normals you have a variety of choices. 50/2, 50/1.5, 35/2, 35/1.4, and 35/2.8 Every one of these optics are world class and any photographer should consider themselves lucky to own one. The 45 F2 is very sharp, but modern tastes would find it's 'bokeh' pattern offensive (I am not one of these people). The ZM 35s mostly are a little smoother in this regard, and no-softer. The 50/2 is one of the sharpest 50s you can get, it's extremely good. The 50/1.5 is more about rendering, it's a special application 50. Best used for portraits IMO.