I have two endoscopes with characteristics: Working length: 175 mm ø = 4.0 mm Angle view = 30 Working length: 175 mm ø = 2.0 mm Angle view = 30 Note that the working lengths are exactly the same, just the external diameter changes (ø = 4.0 mm and ø = 2.0 mm). In spite of the external diameter difference, the involved optics seems to be exactly the same (please confirm if we are right) in both models. is there any difference between internal diameter?