The 45 degree Viewfinder extends the eyepoint without changing the viewfinder image size (as when viewing the cameraŸ??s finder directly- i.e. by x1.0) so that 100% of the camera's finder image can be seen without vignetting even when viewing through housing/mask. The eyepiece is positioned at a 45 degree angle relative to the camera's optical axis which helps in shooting situations like imaging a small subject on the sea bed- by enabling the diver to keep their body off the ground and head at a more natural position relative to the housing. Also the eyepiece rotates 360 degrees to help when shooting vertical compositions- especially from low angles. Anti-reflective multi-coated glass optics for high light transmission and a bright- clear viewfinder image. Lens construction: 4 lens groups with 6 lens elements.