Originally posted by dragra
In my opinion old & cheap zooms are not worth the hassle. They are designed for film, yet dSLR are much more prone to flare and ghosting, so don't expect to get anything but substandard results from such an old lens design.
True for many old manual zooms; zoom technology has just improved tremendously over the decades. Some are still quite usable, especially those with a fixed maximum aperture like my Vivitar-Komine Series 1 70-210/3.5 and Sears-Tokina 55-135/3.5.
But especially Sigma was not known for making quality zooms back then. Even some old Nikon zooms suck. And the Pentax M40-80 and A28-80 and A35-80? Ick! As for flare: Use a hood.