None; the only consideration is that the the field of view of your lens will increase by 1.5x; that is: A 50mm lens will have the same field of view on your camera as a 75mm lens on a full-frame camera. To put it another way, to get the field of view given by a 50mm lens, you'll need to use a 35mm lens (BTW, This applies whether your use FX or DX glass; focal length is focal length).