The straight viewfinder extends the eyepoint without changing 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. Unlike the 45 degree Viewfinder- the Straight Viewfinder is positioned in parallel with the cameraŸ??s finder so viewing replicates the same natural eye position relative to the camera as when shooting on land. This is somtimes better for panning or fast moving subjects. Also- with the straight viewfinder it is possible to make fine distance adjustments between housing and subject by just moving the housing relative to the subject- without readjusting your body position each time- and without losing sight of the subject in the viewfinder. High light transmission anti-reflective multi-coated glass optics provide a bright- clear viewfinder image.