When speaking of glass, the term "Pro" defines high quality. And it make no difference, DX, FX, MX or what ever. As long as the image circle from the glass will cover the sensor it's what ever works! I shot DX for over 6 years and never bought a DX lens. All full frame glass. This thread is a little amusing, the debate should be directed to the OP's question/statement and not the definetion of Pro glass as related to the sensor size. So Pure, don't worry about the crop factor, these are great Pro quality lenses and worth the price. The SB-900 is available at B&H for 399.00 right now, so I would hold off on that.