Contrast, edge to edge clarity, resolution, light transmission, larger sweet spot – across the board, the B Series has a ~5-10% increase in performance. The internal optical system uses a higher grade of glass throughout the entire unit. All glass is produced in Japan. Units are produced individually and undergo a more rigorous inspection. Overall, they are larger and weightier with a magnesium frame and feel more substantial in the hands. These compete against the best optics in the market.