The T-2-star-diagonal is now available with two different mirrors, MaxBright (#2456100) or Bbhs (#2456103), serving different purposes. The MaxBright (#2456100) still is available with their time tested dielectric coating. Alternatively the latest addition to the family is the same housing but with hardened silver with dielectric over coating (#2456103). They tested their new hard-silver coating to be much higher in brilliance than cheap dielectric coatings of other manufacturers. This is the only diagonal mirror of this size made of Sitall-glass ceramics.The latest addition to the Baader Diagonal family. This diagonal has the same casing as the MaxBright Diagonal (#2456100) but with hardened silver with dielectric over coating. This is the only diagonal mirror of this size made of Sitall-glass ceramics. Sitall glass is a crystalline glass ceramic with ultra-low thermal expansion properties, low thermal expansion is a critical feature needed in the manufacture of optical elements for high quality optical telescopes and accessories such as this mirror diagonal..