The Mamyia Sekor E is a rather small and lightweight (310 g) medium telephoto lens for the Mamiya ZE, ZE-2, ZE-X and ZM cameras. Following the original and slightly slower six primes (3.5/28, 1.7/50, 2/50, 3.5/50, 3.5/135, 4/200) , the 2.8/135mm was introduced around 1982 to complement the earlier Sekor E 3.5/135mm. The 2.8/135mm came along with three other "fast" primes, namely the 2.8/28mm, the 2.8/35mm and the 1.4/50mm, and was later supplemented by an astonishingly lightweight E 4/300mm lens. 

The Sekor E 2.8/135mm shares its optical computation with the previous Sekor CS 2.8/135mm for NC 1000 cameras. Like with most other Sekor E primes, its barrel is mainly made from metal; only the focusing and aperture rings are made from polcarbonate. Focusing is slightly stiff, but the lubricants have not dried out. There's an extendible lens hood (metal), and focuing goes down to 1.5 m (common for 135mm lenses). Aperture range is f2.8 − f22.

The Sekor E 2.8/135mm − as its precedessor from the CS series − clearly was optimized for weight. Compared to a Minolta MC/MD 2.8/135mm [4/4] or a Leica R 2.8/135mm, the Sekor E weighs less than 60% (Minolta) or a mere 42% (Leica). That's remarkable, but the consequences can be seen: It has much stronger lateral CAs than most other OEM 2.8/135mm. Surprisingly, the corner resolution is quite good even at f2.8 (and much better than that of the Leica R 2.8/135mm [2nd computation]), but CAs should be removed in postprocessing whenever possible.

The earlier Mamiya SX 2.8/135mm has a different computation. It is much heavier than the Sekor CS and Sekor E lenses, has less CAs and has therefore a superior optical performance (which BTW is among the best vintage 2.8/135mm lenses I know).

The Sekor E 2.8/135mm is pretty rare (as are all the "fast" primes mentioned above). It was introduced late, shortly before the Osawa distributor for Mamiya 35mm stuff collapsed in 1984. Prices can be as high as USD 200.--. If someone is interested in the CS 2.8/135mm − that on is much easier to find, and considerably cheaper. 

MAMIYA SEKOR E /EF135mm 1:2.8:                  (5 lenses /4 elements)