I want a wide angle lens for my Nikon D90 and after reading numerous reviews I think I will go for a Sigma. The only dilemma, which I haven't found an answer for is, which one to go for? The Sigma 10-20mm f3.5 EX DC HSM Lens is slightly more expensive, but what is the advantage/difference over the Sigma 10-20mm f4-5.6 EX DC HSM? I understand the f3.5 is faster, but other than this what are the pros and cons? Thanks
I have borrowed the f/4-5.6 version for some landscapes, but I don't know anything about the new version other than what I've read in reviews.
The original version had quite a bit of distortion at 10mm. From what I can read from reviews (for example this one), the distortion remains (comparison here) and is more complex. This review calls the f/3.5 a "mushy blur" in the corners. Compare that to the f/4-5.6 MTF charts by the same reviewer here where the resolution figures are almost double at 10mm in the extreme corners.
Looking at Sigma's own data on the f/3.5 and f/4-5.6, the optical design looks very similar in configuration, but they have added more ED (low dispersion) type glass, which may reduce chromatic aberration and flare.
From the looks of things, it appears that the main difference really is just that fixed, faster aperture, and some possible variances in distortion and sharpness, which could be important to you if you take lots of pictures of test charts :) If doing outdoor photography and stopping down the lens, there probably isn't much between them. If you do some low light shooting, especially at 20mm, the wider aperture will obviously be helpful.