These cameras were produced by factory "KMZ" (Krasnogorsk) since 1965 up to 1981 and by factory "BeLOMO" (Belarus) since  1975 up to 1988. About 8,000,000 copies were made. Frame size 24X36mm

Lenses (screw mount M39 before 1968): Industar-50 (3.5/50mm), Helios-44 (2/58mm)
Lenses (screw mount M42 after 1968): Industar-50-2 (3.5/50mm), Helios-44-2 (2/58mm)
Lenses for Zenit-E are here

Adjustable shutter speeds - 1/30, 1/60, 1/125, 1/250, 1/500 of a second and "B". The main difference from Zenit-3M: It has selenium lightmeter, mechanism of mirror and lever cock were changed