I recently picked up a Sigma 10-20mm f/4-5.6 ultra-wide-angle lens for my Pentax K-5 II DSLR. On the first day that I took it out, I tried using a 1000x neutral density filter to blur water in a stream. The results were disappointing:
Even though the light was pretty dull, I attributed the bright horizontal streaks to lens flare from the cheap, uncoated filter, and I didn’t think much more about it.
