I am selling a brand new Inon UWL-100 28AD wide-angle conversion lens for $295 + shipping.
US prices are around $430. Lowest is $324.95 from divervision in Taiwan.
This uses a 28AD bayonet type mount, and transforms a 28mm lens into a super-wide.
Details about the lens here: http://www.inon.jp/p...0028ad/top.html
I have also a Adaptor Ring ADF M67 which will screw into a standard 67mm lens thread to allow mounting of a 28AD lens ($10). The combination works great on Nauticam Sony RX100 housing, but vignettes on Meikon Sony RX100 - which is why I am selling.