This advanced, expensive coating can only be found with the very best roof prism viewers from Bynolyt. In a roof prism a phase shift occurs between light beams, which are mirrored from the different prism planes. This has the consequence that a point is not depicted as a point, but as a spot. That gives sharpness and brightness loss. Phase correction coatings eliminate that phase difference, so that the viewer image becomes razor sharp and crystal clear.