Vivitar's 28-70mm range covered the standard-zoom segment through the late 1970s and 1980s with several closely related variable-aperture versions built by different contracted manufacturers, sold as an all-in-one alternative to carrying separate 28mm and 50mm primes.
This f/3.5-5.4 version is a manual-focus standard zoom with a maximum aperture narrowing from f/3.5 at 28mm to f/5.4 at 70mm, offered in the principal manual-focus SLR fittings of the period. Its precise manufacturer, filter thread, weight and minimum focus distance are not confirmed from available sources.
As with most consumer standard zooms of its generation, it favours range and affordability over speed, giving usable results by f/8 but visibly softer corners and lower contrast wide open than Vivitar's Series 1 standard zooms.
It is a low-cost way into manual-focus zoom shooting on the used market today. Buyers should check for smooth, grease-free zoom travel, confirm the aperture ring detents still click cleanly, and inspect the rear element for haze.