The answer is a Nauticam NA-645DF Underwater housing!
The NA-645DF Housing is available for the Phase One & Mamiya 645DF cameras with Phase One P+ Digital Backs (unfortunately it’s not available for the IQ series). This camera and housing package redefines professional underwater imaging, setting new standards for the highest resolution, fastest flash sync speed and greatest dynamic range available in any underwater camera system.
It is designed with the photographers in-water experience in mind. Careful design attention results in intuitive, convenient access to key controls (shutter release, f-stop, shutter speed, AE-L, and four digital back push buttons) from the housing handles.
The housing back is oversized to yield near neutral buoyancy and excellent front-back balance. Configured for the Phase One 28mm wide angle lens with a 9″ glass dome port, the housing is perfectly balanced, and .7kg negatively buoyant. When set up with a flat port system and Phase One 120mm macro, the entire system is .15kg negatively buoyant.
Four mounting points are available for accessory strobes and lights. Two Nikonos, Ikelite, or S6 Flash connectors are included as standard equipment.
Now that’s what you buy a Phase One user who has everything for Xmas 🙂