I am using the Panasonic 8mm behind the Zen Underwater DP-100-EP 100mm Dome Port for Panasonic 8mm FE in Olympus PT-EPxx Housings. Which I like very much. Small, glass and easy to use with good edge sharpness. Got 8mm discounted from Reef and DP-100-EP full price.
I have been shooting the Inon WAL-100 wet lens for a long time and still happy with it