Baader's T-2 BBHS Star Diagonal is machined with T-2 threads, making it compatible with all Baader's Astro T2 system of parts. It provides high reflectance over a wide spectral range, from 390 to 2000 nm, giving you beautiful high color fidelity. The star diagonal is higher in brilliance and has lower scatter than the cheaper dielectric coatings. The BBHS (BroadBand Hard Silver) coating with dielectric protective overcoating provides a high quality shield over the star diagonal, giving you the most vivid observing conditions. The Sitall glass-ceramic zero expansion mirror won't lose its flatness, even during extreme temperature fluctuations.