Voigtländer 21/25mm Viewfinder Black

You place the Voigtländer 21/25mm Viewfinder on the hot shoe of your camera and it is designed for use with a 21mm or 25mm lens. The viewfinder is constructed with 4 lenses and 4 groups, has a magnification factor of x0,42 and a diopter of -1.1.