The PTWC-01 was introduced long ago (in about 2002?) for use on their housings of that era. I have had one since about then. It mounts directly on the M67 ports of many housings, including the Olympus PT-010, PT-015, PT-018, PT-020, PT-022, PT-027, and PT-050 housings, and others with step rings.
At that time most wide lenses were supporting only 35mm or wider camera lenses, but the PTWC-01 was apparently designed for wider lenses. The PTWC-01 is bigger, heavier and more complex optically than the other comparable wet lenses and more expensive too. In short, it was overdesigned. No conspiracy, just lucky for us.
It turns out that a better solution was made by Athena at the time. They made a replacement glass dome port for the C5060 and C7070 which allowed the used of another excellent Olympus wide converter, the Olympus WCON-07c, inside the housing. This was much more practical than trying to add a heavy wet lens to the front of the housing, because of more secure mounting of the port to the PT-027 housing body. It was also much lighter and optically superior as most well designed dome ports are.
Perhaps someone will make a replacement dome port for the PT-050 along similar lines. This locks you into making the whole dive with the wide converter lens, but its performance should be optically superior. It avoids the design problems of a wet mount wide converter, namely having to strengthen the outer glass and have pressure seals.
