Sigma has a long history as a lens maker, having been founded over 50 years ago. In the film era it was best known for relatively inexpensive lenses that undercut the camera makers' own equivalents in terms of price. But this has changed over the part decade or so; while other companies have shifted manufacturing to cheaper locations such as China and Thailand, Sigma has stubbornly refused to move from its factory in Aizu, Japan. This means it can no longer compete in the same way on price alone, and it's therefore switched its focus towards higher-value offerings.