The DRA0003 is a dome port intended for wide-angle and fisheye lenses.
 
To make sure this port is suitable for your lens without extension, measure the distance between the back of the camera and the tip of the lens you intend to use. If the distance is shorter than 165 mm (6,5 inch), you can use the DRA0003 without extension. However, port extension (DRA0004) is required if the measured distance is longer