Oops, I just noticed your other questions.

The viewfinder attaches with the wide end towards the front When you hold it far enough from your face that you see neither the outside or inside surfaces of the finder and the center circles are lined up, it will approximate the field of the 35mm lens. It's for viewing with a diving mask.

The tripod socket is for underwater self-portraiture and taking long exposures of extremely slow moving fish. Just kidding , I'm sure that it is used for attaching flash brackets and hand grips and such.

I have Nikonos V now and I've never scuba dived [dove?, diven?] in my life. I use it in the rain, backpacking, boating, beach, any circumstance that would trash any of my other cameras. That 35mm lens gives really beautiful results above water.

A tip for shooting in the rain: try to find a lens hood that is as deep as possible without vignetting to shield the lens from rain drops and carry some photowipes to wipe them off immediately. Keep it pointed down until you are ready to shoot. A big blurry drop of water on the lens will ruin any shot.