Baader Planetarium's new Broadadband Hardcoated Silver (BBHS) mirror diagonal brings silver into the 21st Century. Silver has always been a superior coating to aluminum coatings (even 'enhanced' aluminum), due to its higher reflectivity across the visual spectrum. However, until now, even overcoated silver mirrors exhibited inferior durability to aluminum. Baader's new proprietary hard dielectric coating process seals and protects the silver layer to give durability the equal of aluminum.
Baader's BBHS dielectric coatings deliver high reflectivity across a wider visual spectrum, resulting in improved color contrasts when compared to aluminum and all-dielectric mirrors. The silver coatings also deliver noticeably less scatter than all-dielectrics, resulting in improved contrast that rivals a top quality prism.
BBHS® stands for Broad Band Hard Silver. When applied onto our Sitall (zero expansion glass-ceramics) substrates, these multiple deposited layers of hard silver are being sealed by a set of dielectric layers to achieve long term durability. With this advance in coating technology our BBHS® coating lifetime equals that of a high quality AlSiO2 coating, matching the durability of standard aluminium coated diagonals (and telescope mirrors) which have been in wide use for many years. The BBHS® spectral bandpass is much wider though, when comparing with our 50 layer all dielectric coatings utilized on the 2" ClickLock Star Diagonals. The all dielectric coating system on the 2" ClickLocks is designed to transport 98 to 99 percent of a spectral window ranging from 400 to ~700 nm - at an angle of exactly 90°. By design, the Baader all dielectric coating system perfectly blocks UV and IR and works as added protective measure when observing the Sun in white light or with H-alpha filters - since only visual wavelengths from 400 to 700 nm will reach focus. BBHS® silver in contrast likewise has 98 to 99% reflective property but delivers a much wider spectral window, ranging from 390 out to 2000 nm - while not being restricted to exactly a 90 ° angle - and with the silver producing absolutely zero scattered light.
With the Baader BBHS® coating a well trained eye absolutely does distinguish more and richer colour on planets such as Jupiter, Mars and even on the moon - especially in conjunction with APO refractors. Predominantly during observation of planetary objects or bright nebulae, even at very high magnification, the BBHS® recipe does intensify colour, especially in the red end of the spectrum. It is quite amazing for many people to learn how very sensitive the human eye really is far out into the UV and NIR - far beyond conventional belief (respectively conventional experience). This experience is not to be had with any sole dielectric or multilayer aluminium reflective coatings and - most noticeable - there is not any trace of haze or stray light as with many other coating systems. The brilliance of the BBHS silver when observing with outstanding optics is simply breathtaking.
The Baader BBHS® coating system is solely applied onto zero-expansion glass (Sitall) and onto the Baader-T-2 36mm and 2" 50 mm 90° prisms, as well as the T-2 and 2" (Astro quality grade erecting) Amici-prisms. In conjunction with the magnesium body of the 2" star diagonal, the Sitall-based BBHS® coating does perform unparalleled, in remaining at thermal equilibrium under all circumstances and in supplying a sharp stable and calm image of previously unknown brilliance.