Since I shoot digital I bought the Sigma lens a Hoya cirkular W-Slim 72mm polarizing filter. Here was the reason, to protect the lens and not very expensive to get high-contrast background shots, especially of heaven.
For exterior shots of the filter is excellent in areas it should, however, again be unscrewed, because the filter out to be a little light eaters.
Furthermore, I will work out only with the lens hood and polarizing filter.
Photos of Strasbourg had suddenly reflections in the image, which I with the analog camera (with polarizing filters) had not earlier. This is a significant effort!
Nevertheless, the acquisition of a polarizing filter is always worthwhile, solely to protect the Objetivs - but not just have to be this price range.
