The basic design of the viewfinder mechanism of the Leica M limits the image field view in such a way that bright line frames for focal lengths below 28 mm cannot be included in any of the viewfinder configurations. In the case of the 0.85X viewfinder the bright line frame for the 28 mm focal length is also no longer possible to include.
To ensure that the wide-angle lenses for the Leica M can be used optimally with all viewfinder magnifications, an accessory viewfinder for 21/24/28 mm lenses is provided. It slides into the accessory shoe, and is secured by a clamping screw. The desired finder field is then selected by simply turning a thumbwheel, which has a click stop at each of the three possible settings. The focusing and exposure control are handled as usual by the Leica M's combined viewfinder/rangefinder.
The viewfinder for 21/24/28 mm lenses is also suitable for eyeglass wearers, since its ocular is rubberized to protect glasses from scratches. As an alternative, it is also possible to use M system correction lenses. When not in use, the accessory viewfinder is housed in a furnished leather case.