Osmo Action 6
Action camera with a variable f/2.0-f/4.0 aperture and a square 1/1.1-inch sensor, waterproof to 20 m as it is.
Specifications
A variable aperture is rare in an action camera and it matters underwater, where the light falls away with every meter of depth. The square sensor is the other half of the idea: one take crops to both a vertical clip and a horizontal one, which suits a dive where you do not get a second pass at the same turtle. Waterproof to 20 m (66 ft) with no case, and the dive set below takes it to 60 m. Video is the job here; for stills of small things a TG-7 will do better.
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