Originally posted by vinceloc Thanks for your input. What I find strange, however, is that the tests done by Photozone.de for both lenses show that CA is higher for the 16-45, and barrel distortion at 16mm for the 16-45 is also higher than 20mm for the 20-35mm. Could it be that your specific lens had some quality issues.
My experience was with my particular FA 20-35mm and my particular DA 16-45mm lenses. I only used one copy of each, so I don't know how much sample to sample variation may have been involved. And note that Photozone tests only one sample on one camera, the lenses tested were used lenses that may have been dropped or jarred, and the tester doesn't use a real optical bench. My FA 20-35mm and DA 16-45mm were both new, and the FA 20-35 was used on both a film and digital bodies.
Also note that I said that the FA 20mm has more barrel distortion at 20mm than the DA 16-45 has
at 20mm. I don't think it is fair to compare the FA 20-25 at 20mm with the DA 16-45mm at 16mm, since there is a huge difference between 16mm and 20mm on a 18x24mm sensor. The DA 16-45 may have a bit more barrel distortion at 16mm, but it is pretty good for this class of lens. It is a 3X zoom with the short range reaching into the ultra-wide. Most lenses in this class have a fair amount of barrel distortion at the wide end, including some expensive Nikon and Canon lenses as well as the Pentax DA* 16-50.
I do think that my FA 20-35 may have had a slight centering defect, because certain shots seemed to have be less in focus on the right side as compared to the left side. But this was not consistent from shot to shot and was only apparent at wider apertures. It may have been due to field curvature. The FA 20-35mm performed much better when well-stopped down, and I tried to use it at f/8 whenever possible. It isn't a bad lens, but I think the DA 16-45mm is better. Even if the image quality was identical, the wider zoom range by itself makes it a much better choice.