Zeiss ZM 35mm f/1.4 Distagon Aperture Series: DeChambeau Barn (Leica SL)
Get the Zeiss ZM 35mm f/1.4 Distagon in silver or black ($250 rebate at time of post). See also my Leica M wish list and Leica SL wish list.
This flat-field subject is a tough test of any lens.
It is also a moiré inducing target, one reason that I strongly dislike relatively low resolution 24MP full frame sensor cameras, whose resolution limits and Bayer matrix sensor are prone to digital artifacts with high performance lensese.
In Guide to Leica in my review of the Zeiss ZM 35mm f/1.4 Distagon:
Aperture Series: DeChambeau Weathered Barn (Leica SL)
Includes images up to full 24MP resolution, over the full aperture range from f/1.4 to f/11.