Introduction
This manual provides essential information for the proper setup, operation, and maintenance of your Celestron 91027XLT Schmidt-Cassegrain C9.25- A XLT (CGE) Optical Tube Assembly. Designed for superior astronomical observation, this optical tube features advanced StarBright XLT coatings and a robust construction for clear, bright views of celestial objects.
Key features include:
- Superior Optics: Features StarBright XLT coatings on its 9.25-inch Schmidt-Cassegrain optical tube, maximizing light transmission for brighter, clearer views of celestial objects.
- Enhanced Visibility: Includes a 6x30mm finderscope to help accurately locate objects, making your stargazing sessions more efficient and enjoyable.
- Versatile Compatibility: Equipped with a dovetail slide bar, this optical tube assembly seamlessly fits CGE mounts, providing a stable platform for precise tracking and observation.
- Optimized Performance: The 1.25" star diagonal and visual back ensure comfortable viewing angles and compatibility with a wide range of eyepieces for customized experiences.
Setup
Proper setup is crucial for optimal performance and safety. Ensure you have a stable equatorial mount, such as a CGE series mount, before proceeding.
1. Attaching the Optical Tube to the Mount
The optical tube assembly (OTA) is equipped with a dovetail rail designed for compatibility with CGE and Advanced Series mounts. Carefully align the dovetail rail with the mount's saddle plate and secure it firmly using the mount's clamping mechanism. Ensure the OTA is balanced on the mount to prevent strain on the motors and for smoother tracking.
Figure 1: The Celestron 91027XLT Optical Tube Assembly, showing its main body and the dovetail rail at the bottom for mounting.
2. Installing the Finderscope
Locate the 6x30mm finderscope and its bracket. Slide the finderscope bracket into the dovetail base located near the front of the optical tube. Tighten the thumbscrew on the base to secure the finderscope. The finderscope aids in locating objects before viewing them through the main telescope.
Figure 2: Side view of the optical tube assembly with the finderscope attached to the top and the star diagonal and eyepiece at the rear.
3. Attaching the Star Diagonal and Eyepiece
Insert the 1.25" star diagonal into the visual back at the rear of the optical tube. Secure it with the thumbscrew. Then, insert the 25mm eyepiece (or any other 1.25" eyepiece) into the star diagonal and tighten its thumbscrew. The star diagonal provides a comfortable viewing angle, especially for objects high in the sky.
Figure 3: Rear view of the optical tube, highlighting the focuser knob, the attached star diagonal, and the eyepiece.
Operating the Telescope
Once assembled, you are ready to begin observing. Always allow the telescope to acclimate to the ambient temperature for optimal image quality, especially when moving from a warm indoor environment to a cold outdoor one.
1. Aligning the Finderscope
Before observing, align the finderscope with the main telescope. Point the main telescope at a distant, stationary object (e.g., a street light or a distant tree during the day). Center the object in the main telescope's eyepiece. Then, adjust the alignment screws on the finderscope bracket until the same object is centered in the finderscope's crosshairs.
2. Focusing
The Celestron 91027XLT features manual focus. To focus, rotate the large black knob located at the rear of the optical tube (as seen in Figure 3). Turn the knob slowly in either direction until the image in the eyepiece appears sharp and clear. For fine-tuning, make small adjustments until stars appear as pinpoints of light.
3. Observing Celestial Objects
Use the finderscope to locate your desired celestial object. Once the object is in the finderscope's field of view, look through the main telescope's eyepiece. You may need to make minor adjustments to the mount's controls to center the object and then fine-tune the focus. Experiment with different eyepieces to change magnification and field of view.
Figure 4: Front view of the optical tube, showcasing the large primary mirror and the corrector plate with the secondary mirror obstruction.
Maintenance
Proper care and maintenance will ensure the longevity and performance of your optical tube assembly.
- Cleaning Optics: Dust on the corrector plate is normal and rarely affects performance. If cleaning is necessary, use a soft camel hair brush or a can of compressed air (held upright to prevent propellant discharge) to remove loose particles. For smudges or fingerprints, use a specialized optical cleaning solution and a clean, soft microfiber cloth. Apply solution to the cloth, not directly to the lens.
- Storage: When not in use, store the optical tube in a clean, dry environment, preferably in its original packaging or a padded case, to protect it from dust and moisture.
- Temperature Acclimation: Allow the telescope to gradually adjust to significant temperature changes to prevent condensation and thermal currents within the tube.
Troubleshooting
| Problem | Possible Cause | Solution |
|---|---|---|
| Image is blurry or out of focus. | Incorrect focus setting; telescope not acclimated to temperature. | Adjust the focuser knob slowly until the image is sharp. Allow the telescope to sit outdoors for 30-60 minutes to equalize temperature. |
| Difficulty locating objects. | Finderscope is not aligned with the main telescope. | Align the finderscope as described in the "Operating the Telescope" section. |
| Stars appear elongated or distorted. | Poor collimation (mirror alignment). | Refer to advanced guides or Celestron's support resources for Schmidt-Cassegrain collimation procedures. This typically involves adjusting screws on the secondary mirror holder. |
Specifications
| Feature | Detail |
|---|---|
| Product Dimensions | 17.4 x 16.3 x 28.7 inches (17.4"D x 16.3"W x 28.7"H) |
| Item Weight | 20 pounds |
| Model Number | 91027-XLT |
| Brand | Celestron |
| Objective Lens Diameter | 25 Millimeters (referring to eyepiece, not main aperture) |
| Telescope Mount Description | CGE Equatorial Mount (compatible with) |
| Focus Type | Manual Focus |
| Finderscope | Reflex (6x30mm) |
| Compatible Devices | CGE series mounts with CGE Dovetail bar |
| Lens Coating Description | StarBright XLT |
Warranty Information
The Celestron 91027XLT Schmidt-Cassegrain Optical Tube Assembly comes with a 2-year warranty. This warranty covers defects in materials and workmanship under normal use. For specific terms and conditions, please refer to the warranty card included with your product or visit the official Celestron website.
Customer Support
For technical assistance, troubleshooting beyond this manual, or warranty claims, please contact Celestron Customer Support. Contact information can typically be found on the Celestron official website or on the product packaging.
It is recommended to have your model number (91027-XLT) and purchase date available when contacting support.
