Davidson Optronics D 523-103 Porro Prism Bench Mark

The Davidson Optronics D 523-103 Porro Prism is used to establish a azimuth reference line. A beam entering the prism will exit exactly parallel upon exiting. Any rotation about the axis parallel to the vertex of the prism will cause no angular deviation on the beam. This enables angular measurement in one axis, without regard to the other axes. All Faces of the BSC-2 prism are flat to within 1/2 fringe, the pyramidal error is limited to 10 seconds of arc maximum, and the Angle between 2 equal faces is 90 degrees +/- 3". The D 523-102 differs from the D 523 in that it has a mirror surface which is exactly perpendicular to the front face located on the right side (as viewed in the photo). The mirror is accessible through a 1 inch aperture machined into the aluminum housing of the prism. This comes in a foam-lined wooden case.