The Tri-Elmar-M 16-18-21mm f/4 Asph was the second time Leica offered three focal lengths for the Leica M in a surprisingly compact zoom lens. Introduced in 2006, almost simultaneously with the first digital M (the Leica M8), the lens was compatible with not only the analogue M range, but also the new digital model – although the focal lengths had to be converted into their small format equivalent, using an extension factor of 1.33 (21-24-28mm).
The Tri-Elmar-M 16-18-21mm f/4 Asph managed to kill two birds with one stone: the M system's existing, wide-angle range was now available for the digital sector in the form of one single lens. At the same time, the lens greatly enhanced the creative potential of the analogue M series, by offering variable field angles from 94 to an amazing 107 degrees.
The Tri-Elmar-M's extreme focal length range required the use of an external viewfinder in order to frame the image with precision.