Celestron Starbright XLT Optical Coatings

Since Schmidt-Cassegrain designs use both mirrors and lenses, obtaining maximum light transmission without sacrificing quality is the key. This is where the StarBright XLT coatings come into play. 

Using a technique known as "vacuum deposition", optical coatings are applied in a thin manner on the optical glass components and positioned properly relative to each other to maximize light transmission. The mirror is coated with metallic coatings that effectively increases light transmission from 4% for mirrors without coatings and 86-88% with standard coatings to a whopping 95%. This is the first step to achieving the necessary light transmission.

The second step is applying the coatings to the lens which is more sophisticated and complex process due to the fact that light is lost in both the reflection and absorption, thus resulting in further light loss. 4% is reflected back intially while more light is lost in the absorption through the glass and second lens surface. To solve this problem, Celestron has implemented dielectric materials known as A/R (anti-reflection) coatings to obtain a very low and flat reflection across the visible spectrum.

Combining these factors results in a remarkable peak transmission of 89% at 520nm and an overall average transmission of 83.5% from 400 to 750nm. The graph below demonstrates this.

The charts below show the improvement of transmission, reflectivity and corrector transmission obtained through Starbright XLT coatings verses previous coatings. It has a peak transmission of 89% vs the previous Starbright peak of 80%. In terms of reflectivity, the XLT coatings have an average peak of 93% vs previous coatings at 91%.

The Starbright XLT corrector transmission is 97.4% compared to other coatings with a lower peak.

Celestron has implemented two methods to test the effectiveness of the StarBright XLT coatings.

The first method is by measuring the optical tube performanec in its entirety. This is done by comparing a beam of light passing through the optical components of the optical tube against a beam of light in air. By dividing the light ratio of the beam through the optical tube verses the beam through air, Celestron can measure the effectiveness and performance. However there are challenges to this method including but not limited to making sure the beam is constant and that light capture is effective, steady and clean and making sure the optical components are properly lined up so they don't skew the results in one way or another.

The second method is easier to execute and simply measures each component's spectrographic performance to make sure all are working properly. This method in addition to not having the setbacks of the first method, also provide greater analysis of each individual component of the optical tube, something not possible in the first method. This method also helps determine the upper limit of the telescope's upper throughput using the calculation below:

%TT = %TC x %RP x %RS

%TT is Total Telescope Throughput

%TC is Corrector Plate Transmission

%RP is Primary Mirror Reflectance

%RS is Secondary Mirror Reflectance

Celestron has implemented two methods to test the effectiveness of the StarBright XLT coatings.

The first method is by measuring the optical tube performanec in its entirety. This is done by comparing a beam of light passing through the optical components of the optical tube against a beam of light in air. By dividing the light ratio of the beam through the optical tube verses the beam through air, Celestron can measure the effectiveness and performance. However there are challenges to this method including but not limited to making sure the beam is constant and that light capture is effective, steady and clean and making sure the optical components are properly lined up so they don't skew the results in one way or another.

The second method is easier to execute and simply measures each component's spectrographic performance to make sure all are working properly. This method in addition to not having the setbacks of the first method, also provide greater analysis of each individual component of the optical tube, something not possible in the first method. This method also helps determine the upper limit of the telescope's upper throughput using the calculation below:

Celestron has implemented two methods to test the effectiveness of the StarBright XLT coatings.

The first method is by measuring the optical tube performanec in its entirety. This is done by comparing a beam of light passing through the optical components of the optical tube against a beam of light in air. By dividing the light ratio of the beam through the optical tube verses the beam through air, Celestron can measure the effectiveness and performance. However there are challenges to this method including but not limited to making sure the beam is constant and that light capture is effective, steady and clean and making sure the optical components are properly lined up so they don't skew the results in one way or another.

The second method is easier to execute and simply measures each component's spectrographic performance to make sure all are working properly. This method in addition to not having the setbacks of the first method, also provide greater analysis of each individual component of the optical tube, something not possible in the first method. This method also helps determine the upper limit of the telescope's upper throughput using the calculation below:

%RS = %RSR x %RR

%RS is Sample Reflectance Factor

%RSR is Reference Standard

%RR is Reference Standard Known Reflectance

Celestron has implemented two methods to test the effectiveness of the StarBright XLT coatings.

The first method is by measuring the optical tube performanec in its entirety. This is done by comparing a beam of light passing through the optical components of the optical tube against a beam of light in air. By dividing the light ratio of the beam through the optical tube verses the beam through air, Celestron can measure the effectiveness and performance. However there are challenges to this method including but not limited to making sure the beam is constant and that light capture is effective, steady and clean and making sure the optical components are properly lined up so they don't skew the results in one way or another.

The second method is easier to execute and simply measures each component's spectrographic performance to make sure all are working properly. This method in addition to not having the setbacks of the first method, also provide greater analysis of each individual component of the optical tube, something not possible in the first method. This method also helps determine the upper limit of the telescope's upper throughput using the calculation below: