An optical system (10) for use in an underwater environment is proposed, wherein the optical system (10) comprises a housing which delimits an interior (60) of the optical system (10) with respect to the surroundings (50) in water-tight fashion, and a lens (20) with an outer surface (24), wherein the housing comprises a mount (40), wherein the lens (20) is received in the mount (40) in such a way that the outer surface (24) of the lens (20) is in fluid contact with water of the underwater environment when the optical system (10) is situated in the underwater environment, wherein the outer surface (24) of the lens (20) has an arched form, in particular a convex form, preferably a spherical convex form, wherein the lens (20) has a first arched contact face (28), in particular a spherical contact face, and the mount (40) has a second contact face (48), wherein the lens (20) is arranged in the mount (40) in such a way that the first contact face (28) presses against the second contact face (48) when the pressure of the surroundings (50) of the optical system (10) is greater than the pressure in the interior (60) of the optical system (10).