I have read a few reports now that say that the Tamron 17-50 has focussing issues, being front focussing at one end of the zoom range and rear focussing at the other end. I dont know if this is confined to a particular period in time, or a problem with particular examples, but it does put me off buying this lens. If it sharp but doesnt focus well, then the results are not going to be great.

I have been thinking also about the Sigma 17-70 - it doesnt have the speed at the longer focal length (but I have a 50mm prime lens) and I havent read anything of the focussing issues, plus it has a larger range and better macro abilities (although I appreciate that neither are proper macro lenses)

I must admit I have got some pretty good results from the 18-55 kit lens, so a part of me thinks why bother?

Any comments, particularly on the focussing issue, are most welcome. I have a K20D, so I know it has the ability to adjust the auto-focus, but unsure whether it would cope with a lens with both front and rear focus issues (at each end of the range).

Cheers

Stuart