The Vivitar 70-150mm belonged to the marque's mid-1970s TX-era consumer zoom range, sold as an affordable step-up telephoto for owners of the period's popular manual-focus SLRs. Like most Vivitar-branded optics of the time it was manufactured under contract rather than in-house.
It is a manual-focus, close-focusing zoom with a maximum aperture that varies from around f/3.8 at 70mm to f/4.5 at the 150mm end, taking 55mm filters, and offered across the manual-focus SLR fittings current in the late 1970s. Precise element count, weight and minimum focus distance are not confirmed from available sources.
Its shorter zoom range compared with Vivitar's 70-210mm and 80-200mm siblings gives a smaller, lighter barrel, which was part of its original appeal, though corner performance and contrast are unremarkable by later standards.
It is an inexpensive find today, mostly bought by collectors of vintage zooms or as a light travel telephoto. Check the zoom action for smoothness, confirm the 55mm filter thread is undamaged, and inspect for the haze and fungus common in 1970s multi-group zooms.