The Mamyia Sekor E 3.5/28mm is a small and extremely lightweight wideangle lens for the Mamiya Z series of SLR. Unusual for its time, it features a pretty outdated lens layout consisting of a master lens (triplet) and a two-lens wide angle converter in front of it. Such constructions − master lens and wide angle converter in front of it − were common in the 1960s, although around 1965 Nikon and Konica were pioneering a more integrated way of looking at the challenges of calculating a good a wide angle retrofocus 3.5/28mm lens.

While it may be more difficult to get a decent performace with the simple basic design chosen by Mamiya, it certainly has its advantages when it comes to costs, size and weight. The barrel of the Sekor E 3.5/28mm is well made. Most parts are made from metal; only the aperture and the focusing ring are made from plasics. There is no rubber grip, and usually the lubrication of the focusing thread has run dry. The resulting feeling of a "cheapo" lens is somehow undeserved, and re-lubricating results in a much better haptics. That said, other contemporary 3.5/28mm primes (Konica AR, Minolta MD, Nikkor Ai) do feel more solid, but are also much heavier.

The Mamiya Sekor E 3.5/28mm has a better performance than the "old-style" constructions from the early 1960s (e. g. Minolta MC-I 3.5/28mm [7/7]), but it's inferior to the more modern [5/5] constructions with their  "intergated" optical design (i. e. not separate master lens + wide angle converter). Those lenses have considerably less coma and astigmatism.

Wide open, center performance is excellent even on 43 MP full frame cameras. Borders and corners have a low resolution though. Stopping down to f8 or better f11  is required for a good performance on 24 MP cameras. At f11 and on 43 MP FF the corners are still not perfectly sharp (comparable to the Minolta MD 3.5/28mm); the Konica AR 3.5/28mm [5/5] and the Nikkor Ai are slightly better in this regard.

Plenty of Mamiya Sekor E 3.5/28mm lenses are easily availble; here in Switzerland they go for < CHF 20.--, but current (2023) e-bay prices are clearly higher (USD 40 - 80.--). 

The Mamiya Sekor E 3.5/28mm is a perfect lightweight landscape lens, as long as you can use f11 and don't need to go beyond 24 MP FF. While the difference in speed between the Sekor E 2.8/28mm and the Sekor E 3.5/28mm may look negligeable, the f2.8 version has a better performance in the f2.8 to 5.6 range and thus is more versatile than the slower f3.5 cousin.

MAMIYA SEKOR E 28mm 1:3.5                  (5 lenses / 5 elements)