Lens correction with wide angle lenses is needed to compensate for the steep ray angle to the sensor, which result in color casts moving away from the cent of the frame (see the Zeiss 21mm f/4.5 Biogon examples for a worst-case scenario). This issue is inherent to the Leica M lenses on digital sensors.
Both the Leica M9 and the Leica M Typ 240 have such correction built-in for all Leica M coded lenses. Other brands can “pretend” to be Leica M lenses via the Coder Kit, and this can work well in some cases.
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