StarBright XLT is a revolutionary optical coating from Celestron that outperforms any other coating in the commercial telescope market. The Schmidt-Cassegrain and EdgeHD telescopes come as standard with this high-quality optical coating, making for an incredible performance and value.
One of the most important factors in the evaluation of a Schmidt-Cassegrain/EdgeHD telescope’s optical system performance is its transmission, or the percentage of incoming light that reaches the focal plane. The design of the StarBright XLT system accomplishes a crucial objective: a coating system optimised for both visual use and for CCD/photographic imaging.
There are three major components that make up our StarBright XLT high-transmission optical system design:
- Unique enhanced multi-layer mirror coatings made from precise layers of aluminum, SiO2 (quartz), TiO2 (titanium dioxide), and Si02 (silicon dioxide). Reflectivity is fairly flat across the spectrum, optimizing it for both imaging and visual observing.
- Multi-layer anti-reflective coatings made from precise layers of MgF2 (magnesium fluoride) and HfO2 (hafnium dioxide). Hafnium—a rare element that costs nearly £1200/$1,500 per kilogram—gives a wider band pass than titanium that is often used in competing coatings.
- High-transmission water white glass is used instead of soda lime glass for the corrector lens (plate). Water white glass transmits about 90.5% without anti-reflective coatings; that’s 3.5% better transmission than uncoated soda lime glass. When water white glass is used in conjunction with StarBright XLT’s anti-reflective coatings, the average transmission reaches 97.4%: an 8% improvement.*
These three components of our StarBright XLT coatings result in one of the finest coatings available. The peak transmission for the systems is 89% at 520 nm. The overall system transmission is 83.5% averaged over the spectrum from 400 to 750 nm. The plot below shows the entire system transmission over the spectrum:
Often people ask about what improvement there is over the StarBright coatings on older Celestron SCT models. In general the StarBright XLT coatings give approximately a 12% improvement over the older StarBright transmission.** StarBright XLT has peak transmission at 99%, while StarBright peaks at 91%.
**Percent differences are calculated by taking the comparison data percentage divided by the baseline data. Example: measured average system transmission for current StarBright is 72%. StarBright XLT average system transmission is 83.5%. 83.5% divided by 72% = 1.16 or 16% improvement. Measurement results are rounded to the nearest whole percentage.