The Celestron C9.25 Optical Tube Assembly (OTA) sits in a unique spot with its 9.25-inch aperture and 2350 mm focal length, often regarded as the "just right" size for many astronomy enthusiasts. This durable aluminum tube weighs a manageable 20 pounds and measures 22 inches, making it convenient for transportation and setup. Despite its compact form, the tube delivers remarkable views, thanks to its f/10 focal ratio and the option for Fastar technology (explained further below).
The tube is coated with Celestron's exclusive StarBright® XLT optical coatings. These coatings notably enhance contrast and light transmission, resulting in brighter deep-space images and reduced exposure times. With StarBright XLT, you'll see finer details on the Moon, planets, and dim celestial objects like galaxies and nebulae.
Compatibility is also a strong suit for the Celestron C9.25. It can be attached to a wide variety of computerized telescope mounts, owing to its CGEM-style dovetail bar. Overall, this OTA provides an optimal blend of portability, user-friendliness, light-collecting capability, and cost-effectiveness for amateur astronomers.
About Fastar Technology
Back in 1997, CCD cameras started to eclipse traditional film photography in the astrophotography arena. Celestron partnered with Santa Barbara Instruments Group (SBIG) to introduce Fastar. This game-changing addition to Celestron's Schmidt-Cassegrain Telescopes (SCTs) allows users to remove the secondary mirror and replace it with a specialized field-flattening lens assembly (sold separately). This permits the use of a CCD camera right at the telescope's f/2 focus on the primary mirror. The big win here? Exposure times can be 25 times shorter than at the default f/10 focus, enabling 30-second snapshots of galaxies and nebulae.
Breaking Down StarBright XLT Coatings
Celestron's StarBright XLT is an industry-leading optical coating system, outshining its competitors. It consists of three main elements:
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Multi-Layer Mirror Coatings: Made of meticulously layered aluminum, SiO2 (quartz), TiO2 (titanium dioxide), and SiO2 (silicon dioxide), these coatings achieve balanced reflectivity across the light spectrum, making it ideal for both visual observation and imaging.
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Anti-Reflective Coatings: Crafted from MgF2 (magnesium fluoride) and HfO2 (hafnium dioxide), these coatings broaden the band pass. Hafnium, although pricey, significantly outperforms titanium used in other coatings.
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High-Transmission Glass: The corrector lens employs water white glass that allows 90.5% light transmission without any coatings. This is an improvement of 3.5% over conventional uncoated soda lime glass. Paired with StarBright XLT coatings, light transmission impressively soars to an average of 97.4%.
For more in-depth info on StarBright XLT coatings, you can visit Celestron's dedicated webpage.
Specifications
| Optical Design: | Schmidt-Cassegrain |
| Aperture: | 235mm (9.25") |
| Focal Length: | 2350mm (93") |
| Focal Ratio: | f/10 |
| Focal Length of Eyepiece 1: | 25mm (0.98") |
| Magnification of Eyepiece 1: | 94x |
| Finderscope: | 6x30 |
| Star Diagonal: | 1.25" Star Diagonal |
| Optical Tube: | Aluminum |
| Highest Useful Magnification: | 555x |
| Lowest Useful Magnification: | 34x |
| Limiting Stellar Magnitude: | 14.4 |
| Resolution (Rayleigh): | 0.59 arc seconds |
| Resolution (Dawes): | 0.49 arc seconds |
| Light Gathering Power (Compared to human eye): | 1127x |
| Secondary Mirror Obstruction: | 85mm (3.35") |
| Secondary Mirror Obstruction by Diameter: | 36% |
| Secondary Mirror Obstruction by Area: | 13% |
| Optical Coatings: | StarBright XLT |
| Optical Tube Length: | 559mm (22") |
| Optical Tube Diameter: | 271.78mm (10.7") |
| Optical Tube Weight: | 20 lbs (9.07 kg) |
| Dovetail: | CGE Dovetail Bar |
| Solar Warning |
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| California Residents |
WARNING: Cancer and Reproductive Harm - www.P65Warnings.ca.gov. |
Software and Documentation
9.25" Schmidt-Cassegrain Optical Tube Assembly Dimensional Drawing