I have ambivalent feelings about this lens. Yes, it's about 2/3rd faster than the kit lens, has a greater zoom range, and is relatively cheap, but there are problems at the wide end with vignetting, distortion, softness & particularly CA. These can be corrected in PP, but it would be nice if the design was sophisticated enough not to need that much help.
The lens should not really have the f/2.8. It's very soft at the edges. Here are 3 comparison shots, all taken at 17mm FL & f/2.8.
The first comparison shot shows:
Top: the uncorrected shot
Bottom: CA, vignetting & distortion correction preset I created for this aperture & FL combination in Silkypix Pro 4.
You can see that the distortion is very obvious. The top is a little darker (shaded by the overhand of the roof more), but it looks a different shade too.
The second comparison compares the centre uncorrected area, with the uncorrected top right & the corrected top right.
1. The corner softness is very obvious
2. So is the CA. This is easy to notice even in the shop - I tried 2 copies of this lens and they both have obvious CA.
3. The vignetting can be seen, but I think the roof shading makes a difference here too.
Finally, the bottom right corner. Again, the centre uncorrected area, with the uncorrected bottom right & the corrected bottom right.
The lens is still soft, but not as soft as the top right.
Dan.