Whether youre looking to build a telescope system from scratch or wish to upgrade your kit star diagonal the altair astro 125 inch dielectric star diagonal offers 99 reflectivity due to its multi layer dielectric coatings and extreme durability thanks to its cnc machined aluminium casing the barrel is threaded for attaching additional filters and it has an internal blackened thread to stop stray light reflection increasing image contrast it has a non marring brass compression ring to