Brings the zoom to the equivalent of 170mm. Very impressive for such an affordable telephoto lens (not a zoom, but you can still play withe the zoom a bit until a black circle starts reducing your view). It can be very useful sometimes, to bring into clearer view, things that are a bit too far away. The f value will not be at f2 anymore, because you must use this lens fully zoomed in. You can play with the zoom a bit to obtain some interesting artistic shots. I love this very good lens. I have experienced bad lenses and this one is not one of those.