I just recently purchased a Canon A640 with the Ikelite housing. The housing has the ablility to add a wide angle lens that has a 67 mm screw in thread. I also have a few older Sea & Sea lenses (16mm and Macro 2T). On both lenses it is possible to unscrew the bayonet mount. Does anyone know if I can convert these to 67 mm threaded mount? Will this work? If so, where can I get the threaded mount? Could I use a step down ring? Thanks.