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Celestron - C9 1/4A 9 1/4 inch Optical Tube Assembly, with Dovetail Slide Bar for CG5 mounts & StarBright XLT Coatings
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$ 1260.00
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9 1/4” Schmidt-Cassegrain, 2350 mm focal lenght (f/11), Starbright coatings, 6 x 30 finderscope,
25 mm Plossl eyepiece (94x) 1-1/4”, Star diagonal 1-1/4”, Visual back 1-1/4”, Dovetail slide bar,
Aluminum Optical Tube.
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.
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