Opteka HD² .35x Super Wide Angle Macro Lens Hypergone "Fisheye" For Canon EOS 1D, 5D, 7D, 10D, 20D, 30D, 40D, 50D, 60D, 300D, 350D, 400D, 450D, 500D, 550D & 1000D SLR Cameras (electronic appliances)
This goal is fixed on another goal and can be used directly with a reflex enclosure. Moreover, it is not compatible with the Sigma 18-200 .. you have to buy an adapter. Otherwise, on a 18-55, it works very well.