Vivitar's 28-50mm f/3.5-4.5 was a compact wide-angle standard zoom from the 1980s, aimed at SLR owners wanting a wider everyday range than a typical 50mm prime without stepping up to a large-ratio superzoom. It filled a modest niche in the brand's extensive zoom lineup.
It is a manual-focus zoom with a variable maximum aperture running from f/3.5 at 28mm to f/4.5 at 50mm, coupled to an automatic diaphragm for open-aperture metering. As with most Vivitar lenses of the era, it was manufactured across several interchangeable SLR mounts.
Its short zoom ratio keeps optical compromises modest compared with longer-range Vivitar zooms, giving reasonably even sharpness and contrast across the range for a budget lens. It is better suited to landscape, architecture and general shooting than to isolating distant subjects.
This is one of the less commonly encountered Vivitar zooms secondhand, likely reflecting lower original sales against more popular ranges. Check the zoom and focus rings for smooth operation, look for haze between elements, and confirm the mount fitting before buying, as several were produced.