This is a well-built telephoto zoom lens with a relative large maximum aperture of f/3.5 (@ 80 mm) respectively f/4 (@ 200 mm). Sigma named it “High-Speed Zoom” and in the manual it states that it is the brightest lens in its class.
The lens has a one-touch zoom/focus control system for easy and quick operation. The lens was originally provided with a special close-up lens which reduces the minimun focusing distance to 0.6 m thus enabling a maximum magnification of 1:2. There´s a special compartment in the lens case for that close-up lens.
The optical quality of this lens is excellent. It is already sharp from corner to corner wide open.