Christmas is the season of lens buying. This year I decided that I was going to be bought the Tamron 17-50 f2.8, as it gets rave reviews, I have seen some very sharp results from a friend’s version (on Sony) and I found it for £230 from Amazon Germany. At that price it is a pretty good deal and Amazon is a pretty reasonable company for returns. It took a couple of days to arrive, but within the week I had it strapped to the front of the K5 for a bit of a test. Leafless trees are a pretty good test for a lens. I liked the additional brightness in the viewfinder. Not as good as using the 1.4 or 1.8 lenses, but enough to notice, especially when comparing it to the long end of the Sigma 18-125 f3.8-5.6.
Results were not so good though. In the centre of the frame it was pretty sharp at f2.8, so focus was not a problem, but it was not startling in comparison to the Sigma 18-125. Out on the edges, it was not good. Visible vignetting and quite bad smearing of detail. Even by f4 it was only just matching the 18-125 at nearly wide open (as shown in the attached pictures). In addition, the reach of 125mm is nothing to be sneered at in a general zoom, and as you can see from the third image, the Sigma is pretty good at the edges wide open at that focal length. Maybe this is just a bad example, but it went back and I think I will stick with the 18-125 and consider a nice prime for the critical stuff.