Bubbble ... bubble ...
My underwater camera, a 35mm (film) Nikonos V, is a rangefinder.
Probably due the the UW application, it doesn't have any short of range-focus assistance (eg, split screen to allign, etc) in the viewfinder.
Instead, there's range markings on the lens. On the 3rd party lenses, its a simple knob with values and a tickmark, but on the genuine Nikkor lenses, it has two "pointers" that are hooked into the f/stop: as you go to a higher f/number, the pointers move apart, indicating the total depth of field.
You can get a decent view of this system at
this webpage.
In the above URL's second photo (orange body) looking at the front face of the lens, the top scale (silver) is for focus range (and has two orange pointers) and the bottom scale (black) is f/stop.
The current setting is f/22 and a range of roughly 5 to 7ft (red numbers), or 1.5 to 2 meters (black numbers)...call it roughly 6ft focus distance with +/- 1ft worth of depth of field.
FWIW, with the 15mm wide angle at roughly 0.7m at f/8, the depth of field is roughly 10 inches to infinity.
-hh