Two products in one convenient package compatible with a variety of zoom lenses including the popular canon 17 40mm and nikon 18 70mm the injection molded acrylic 8 inch diameter dome is specifically designed for underwater photography to provide superior optical performance compared to a smaller 4 or 6 inch diameter dome the larger diameter reduces edge distortion on pictures taken with certain super wide angle lenses and makes shooting over under shots half in half out of the water easi