Sigma's 28-200mm f/3.5-6.3 followed the maker's original 28-200mm superzoom with a later, more affordable version of the same one-lens-does-everything concept, sold through the 1990s autofocus era.
The lens spans wide-angle to medium telephoto with a maximum aperture from f/3.5 at 28mm dropping to f/6.3 at 200mm. Sigma made it for Canon EF, Nikon F, Minolta A and Pentax K autofocus mounts as well as Sigma SA, in a lightweight plastic-barrelled design with a screw-type or push-pull zoom mechanism depending on the production run.
The slower long-end aperture compared with the earlier f/3.8-5.6 version made it cheaper to build but dimmer and slower to autofocus in low light at 200mm, a trade-off buyers of the era accepted for the convenience of an all-in-one travel zoom.
Common and inexpensive secondhand. Check the barrel for wobble or zoom creep, a frequent issue on superzooms of this class, listen for a noisy or hunting autofocus motor, and inspect the front element for scratches typical of a much-used travel lens.