The scope
It is always exposed to Sea Pressure. So it does not matter what depth in relation to the scope itself. The issue is the capabilities of the Hydraulic plant (and pressure) or the electric motors in raising the scope. BTW it is pretty much black after about 400 feet or so. Modern systems have diffculty with deeper than typical depths (say about 200 feet or so). One factor that is never modeled accurately is the Vibration of the scope at speeds greater than say 7 knots when the scope is raised deeper the PD. There is no fairing and so it is just the scope dealing with the water flow.
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