The Vivitar 70-200mm f/3.8 belonged to Vivitar's constant-aperture telephoto zoom family of the mid-to-late 1970s, sold alongside the closely related 70-150mm f/3.8 and 75-205mm f/3.8 models as part of the same close-focusing auto-zoom generation.
It is a manual-focus zoom holding a near-constant f/3.8 maximum aperture across its range, with close-focusing built into the zoom barrel, and was produced in the principal manual-focus SLR fittings sold by independent dealers of its era. Weight, filter thread, element count and precise minimum focus are not confirmed from available sources.
The constant f/3.8 aperture gives more consistent exposure and a brighter finder through the zoom range than Vivitar's later variable-aperture telephotos, at the cost of a larger, heavier barrel typical of 1970s constant-aperture designs.
Secondhand prices are modest, reflecting its status as a period consumer zoom rather than a Series 1 optic. Check the zoom action for smoothness and the aperture ring for even click detents, and inspect the elements for haze common in lenses of this vintage.