Welcome to Nikonians! The focal length of FX lenses and DX lenses are the same. DX lenses project a smaller image circle at the sensor plane than FX lenses. Since the sensor plane is in the same location on both FX and DX bodies as well as film bodies the "1.5 X crop factor" applies to All lenses when they are mounted on a DX body. Good Luck and Enjoy your Nikons!