35mm f1.4 M System Mount Summilux Aspherical/ASPH.

Aspherical surfaces indicated by pointers.

The most striking outwardly obvious feature of either of these optically highly similar lenses is the very dramatically concave curvature of the exterior surfaces of both the front and rear elements:

The first, named the "Aspherical", is regarded in the marketplace as superior and it commands a premium price carryover from when it was the original such lens offered by Leica. The design correction that this lens commands is so radical that it is unable to be achieved by a practicably physically ground curvature. Leica's initial approach was to split the correction between two nearly symmetrically placed surfaces at the second and last internal glass/air interfaces. Arguably the only reason why the aspherical correction was not incorporated into a single element is the great difficulty of controllably achieving such a radical curvature pitch rate of change by traditional/classical lens glass grinding techniques.

The second design embodiment, the ASPH.

employs a single "press molded" highly curve shaped aspherical surface on the very first rearward glass/air surface just after the lens center. This approach introduced an approximately 25% reduction in lens production cost with no apparent quality penalty and Erwin Puts has said " The fingerprint differences (between the two) are really very small, if measurable and I would not be put to the test to identify which lens is used when presented with some pictures."