Considering to buy either lens. The range that I need is the 17-55, but I am a bit reluctant to aquire a DX format lens as a long term investment. The question is: will the DX format stay in pro level cameras? with the cost of technology going down and cometition getting much higher, I am arguing that that the next camera after D300 would most probably include a FF sensor. This brings me back to my original question: Will the DX format lenses be redundant for professional grade cameras in a year or two?