Decentring is not measurable. It is by a great distance the best 21mm in the Leica stable and the only choice for the person who needs superior performance from a 21mm lens, with aperture of 2.8. A 21mm lens by nature shows a great deal of empty foreground, which could be filled with some objects close to the lens. The essence of the 21mm is the enclosure of an interesting foreground motive by a large space. It is of importance to see how the lens behaves at distances around 1 meter.
Contrast is low at all apertures.
Overall contrat at full aperture is visibly higher, but it is the micro contrast that produces small details with a high level of crispness. The Elm however reproduces very fine detail just a shade crisper. At full aperture overall contrast is higher than the Elmarit-M 2,8, but more important the high level of micro contrast gives a clear and finely rendering of very fine image details over the whole field, including the extreme corners. Quite impressive is the even performance from center to corner over the whole aperture range. The Super Angulon 3.4 at full aperture is quite prone to flare, it gives large halos around light sources.