The Sigma 17-70mm F2.8-4.5 can focus closer than any other lens and get 1:2.3x maximum magnification.

Do you remember how you had digicams with super macro modes? This feels like it. You can go REALLY close to something at the 17mm end! You can really touch the flowers with your lens! You can put your lens against a computer screen!

Of course, if you want F2.8 at 50mm then the Tamron 17-50mm F2.8 is cheaper. I cannot comment on the sharpness compared to the 17-50mm but the 17-70mm is sharp.

The Tamron 17-50mm F2.8 comes with a Tamron micro-motor in the Canon and Nikon versions (so it sounds like a Transformer buzzing inside.) The Sony and Pentax versions are screw-driven and they are a lot quieter, but not as quiet as a Canon USM or Nikkor SWM.