StarBright XLT — An Optical System Breakthrough!
Celestron has brought its renowned StarBright
technology to an even higher level of light transmission with
the introduction of our new optional StarBright XLT High Performance
Optical Coating System.
StarBright XLT Optical System Design — You’ll
See The Light.
One of the most important factors in the evaluation
of a Schmidt-Cassegrain telescope’s optical system performance
is its transmission — the percentage of incoming light
that reaches the focal plane. The design of the XLT System
accomplishes two crucial objectives: Develop a coating system
that is optimized for visual use and for CCD/Photographic imaging.
The StarBright XLT System — What Makes It Different Makes It Better
There are three major components that make up our StarBright
XLT high transmission optical system design:
1. Unique enhanced multi-layer mirror coatings
Our mirror coatings are made from precise layers of Aluminum
(Al), SiO2 (quartz), TiO2 (Titanium
Dioxide), and Si02. Reflectivity
is fairly flat across the spectrum, optimizing it for both
CCD imaging and visual use. Click here to see a plot of the
reflectivity of XLT’s Mirror
Coatings.
2. Multi-layer anti-reflective coatings
Made from precise layers of MgF2 (Magnesium Fluoride), and
HfO2 (Hafnium Dioxide) A rare element costing nearly $2000
per kilogram, Hafnium gives us a wider band pass than Titanium,
used in competing coatings. Click here to see a plot of XLT’s
corrector transmission.
3. High Transmission Water White glass
Celestron Schmidt-Cassegrain optical systems with optional
StarBright XLT coatings use Water White glass instead of
Soda Lime glass for the corrector lens. Water White glass
transmits about 90.5% without anti-reflective coatings. That
is 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! Click
here to see a plot of water white glass versus soda lime.*
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.
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| This plot is obtained by measuring the reflectivity of
the secondary mirror and the primary mirror and measuring
the amount of light transmitted through the coated corrector
lens. Each of those values are multiplied together calculate
the system transmission. The overall system transmission
peaks at 88.9% while the average transmission is 83.5%
over the spectrum from 400 to 750nm. |
*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%. 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.
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