This is the same 2-inch Star Diagonal that comes with the Tele-Vue 85 and the Pronto. Exquisitely crafted to fold light exactly 90 degrees. The mirror blank is polished to 1/10th the wavelength of light and vacuum coated with enhanced aluminum 96 percent reflectivity. Then it's overcoated to protect the delicate mirrored surface. To ensure the optical alignment of the diagonal, the body is CNC machined from one solid block of aluminum. For maximum contrast anti-reflection threads are cut into the inner surfaces, and 48mm filter threads are included. All 2" diagonals feature brass clamp ring for extra secure, no-mar operation.