72 mm ring with lens port adapter, fits D-A, D-AX, U-A, U-AX, U-AXP, U-B, U-BF, U-BZ, C-AF, C-AFX The patented CA system was invented and developed by ewa-marine to allow the lens of a camera to be fixed to the front port of a housing or rain cape. It ensures that the surface of the lens and that of the housings front port are permanently parallel to each other, thus ensuring that there are nor reflections or other optical disturbances between these two glass surfaces. Due to the CA system, the front port has the same effect as a clear glass filter would have in every day photography. Description: The CA system is composed of an filter-ring and a fixing-ring For video housings we generally supply the appropriate ring for the most popular camcorders. Due to the enormous range of camcorders and the fact that some manufacturers chose obscure, new filter threads for every new model, you might have to purchase an additional reduction adapter to fit the CA system to the filter thread of your camcorder. These reduction adapters are available from every well stocked photo dealer. A tip for users of Panasonic camcorders and their generics: In some cases it would seem, that the camcorder does not have a filter thread! This is not true. For design reasons the manufacturer has fitted the camcorder with a dummy that is screwed into the tread. Turn and unscrew this lens surround (normally chromed plastic) to gain access to the filter thread.