The Leica Tri-Elmar-M 16-18-21mm f/4 Aspherical Lens gives incredible versatility & optical brilliance to the Leica shooter who doesn't need the higher speed of the single-focal-length lenses. The Tri-Elmar is not a zoom, but a three-focal-length lens offering 16mm, 18mm and 21mm choices with a simple twist. Due to the minimal distortion and barely perceptible field curvature, it can be recommended for highly demanding architecture photography even at the 16mm setting. Used on the digital M8, it produces the image effect of a 21 - 28 mm lens, still enabling extreme wide-angle views.
This lens has been updated with the "6-bit" coding, which allows the digital M camera to read this information optically and to identify which lens is being used. The camera can then (optionally) apply a "final stage" software-based vignetting correction (for RAW images the lens used is simply recorded, no change is made).