The Mamyia Sekor E 3.5-4.5/28-50mm is a surprisingly small wide-to-normal zoom lens for the Mamiya Z series SLRs (ZE, ZE-2, ZE-X and ZM). It's barrel is completely made from metal, and it feels pretty solid and sturdy. Focusing and zooming is done by one one ring. Its minimal focusing distance (MFD) is 0.6m, and it doesn't have any macro mode.

Its optical construction - nine lenses in eight elements - is similar to the classical two-group 35-70mm zooms, and its optical performance is as good or even better than most contemporary 28-85mm zooms i'm aware of. The lens clearly is optimized for the 28mm and 35mm range; at f=50mm its performance is a bit lower and not on par with contemporary primes. At the shorter end, though, and especially stopped down, it is pretty usable even on 24MP full frame cameras.

That said, the large and heavy Yashica ML 3.5/28-50mm is clearly better than the much smaller an lighter Mamiya zoom described here.

Generally most 28-50mm (-55mm) lenses are pretty scarce, and the Mamiya 28-50mm is quite difficult to find. Nevertheless prices should be quite affordable since not too many people are collectring Mamiya Sekor E lenses. 

MAMIYA SEKOR E 28-50mm 1:3.5-4.5                  (9 lenses / 8 elements)