Olympus's compact OM wide zoom — the S-Zuiko Auto-Zoom 28-48mm f/4, constant aperture.
The Olympus OM-System S-Zuiko Auto-Zoom 28-48mm f/4 is a compact wide-to-normal zoom for the Olympus OM mount, introduced in 1983. The S-Zuiko prefix denotes an Olympus element code and the Auto-Zoom token marks it as an automatic-diaphragm zoom. It covered a short but useful wide-angle range in a small package, suiting the OM system's compact ethos.
This is a manual-focus Olympus OM zoom with a 28-48mm focal range and a constant maximum aperture of f/4, designated S-Zuiko Auto-Zoom. The constant f/4 aperture holds across the zoom range, and the modest range kept the lens compact. The verifiable specifications are the 28-48mm focal range, the constant f/4 maximum aperture and the manual-focus OM mount; element count, filter thread and weight are omitted rather than guessed.
A 28-48mm zoom spans from a useful wide-angle to just short of normal, covering the everyday range for landscapes, travel, interiors and street work in one compact lens. The constant f/4 aperture keeps exposure steady as the focal length changes, which is convenient for manual metering. It is a practical single-lens solution for wide-to-standard shooting without carrying multiple primes.
This zoom is moderately common on the used market and generally affordable. Check the glass for haze, fungus and internal dust, and confirm the aperture blades are dry and clean. Test the zoom and focus actions for smooth, even movement with no wobble, and verify the aperture ring clicks positively. It adapts to mirrorless as a small, convenient wide-to-normal zoom, though its short range is a consideration versus a modern kit lens.