I had so many disappointments with the Leica 50mm f/1.4 Summilux-SL ASPH in the field; nearly every comparison I made to the the Panasonic 50mm f/1.4 could not really be used. The lens can make really lovely portraits and certain other images. Bought on that basis, it is sure to please.
This aperture series from f/1.4 through f/5.6 looks at the pronounced field curvature of the Leica 50mm f/1.4 Summilux-SL ASPH, showing why the lens is a exceedingly poor choice for landscape work at a distance, or for any planar subject. In diglloyd L-Mount Mirrorless:
Includes images up to full sensor resolution, plus crops.
A lens that cannot render sharpness across the frame even at f/5.6 means that it has no versatility, as it cannot be relied upon to perform for any image where sharpness must cover the frame, or for any planar subject, or for astrophotography. The Leica 50mm f/1.4 Summilux-SL ASPH is such a lens, clearly designed for purposes at odd with general purpose photography. Leica calls it a “reference lens”, which is a remarkably warped claim.
Below, a very utilitarian scene in yuck lighting, but excellent at showing lens behavior.