The Mamyia Sekor E 3.5/50mm Macro lens is a very well made macro lens going from infinity to 1:2 (and 1:2  − 1:1 with the dedicated macro adapter). It seems to have the same optical layoout as the earlier Sekro CS 3.5/50mm Macro, but direct comparison with its predecessor reveals a better performance. As with the 1.4/50mm lens, Mamiya seems to have re-calculated the lens while transiting from the CS to the E/EF mount!

The Sekor E 3.5/50mm was among the first seven lenses manufactured / marketed for the then new Mamiya ZE (1980). Around 1975-1985, short (50mm to 60mm) macro lenses usually had five or six lenses, and they were Xenotars (Mamiya 2.8/60, Nikkor 3.5/55, Olympus Zuiko 3.5/50, Topcor RE 3.5/50, Yashinon 2.8/60mm), Planars (Minolta 3.5/50, Nikkor 2.8/55mm, Zeiss CY 2.8/60mm) or Planar/Plasmat hybrides (Canon FD/nFD, Yashica ML 2.8/55mm). Among all these macro lenses the Mamiya E 3.5/50mm is uniqe, being an inverted Xenotar design.

Back in their time, most short macro lenses were marketed as high perfromance universal lenses: They were ment not only for close-ups, but for landscapes as well. Testing the lenses mentioned above reveals that they are well suited for landscape purposes indees. Stopped down to f5.6 or f8 these lenses (including the Mamiya) have an impeccable performance even in the extreme corners of modern 24 MP FF cameras. No CAs are visible.

Wide open, the Sekor E 3.5/50mm has perfect resolution and no color fringing in the image center, and the borders are sligthly inferior (pixel peeping). Only the corners have a bit less contrast. At infinity, the Mamiya performs better than other famous macro lenses such as the Nikkor Ai 3.5/55 or the  Minolta MD 3.5/50mm, let alone the Konica AR 3.5/55mm (which is an outdated [4/3] Tessar construction). Differences mainly can be seen in the corners; otherwise the competitors are nearly identical.

At closer distances (1:10) all these lenses are near optimum. I have compared about 20 short macro lenses side-by-side, and the results can be found elsewhere. 

MAMIYA SEKOR E 50mm 1:3.5 Macro                  (5 lenses / 4 elements)