Sony 16-50 f2.8 or Tamron 17-50 f2.8 ? (A57)

Depends on your needs and your money. You ain't gonna see any difference till you don't print on large format. Both have close sharpness colors but Sony is better .I tested both lenses for a long time and still couldn't justify ,for my needs ,the price diff that I would pay for the Sony, so I ended up with the Tamron. If you dont do prints and money diff is no pb than go with the Sony . If you will view your photos just on monitor and do ocassional small prints than buy the Tammy . Tamron look rly ugly compared to the Sony but performs the same .