Sky-Watcher EvoStar 120 APO Doublet Refractor Telescope Instruction Manual

1. Introduction

The Sky-Watcher EvoStar 120 APO Doublet Refractor telescope is designed for both visual astronomy and astrophotography, offering superior optical performance. This instrument features a matched doublet objective lens with a synthetic fluorite element, which contributes to excellent color correction and sharp image delivery. The optical tube is equipped with proprietary Metallic High-Transmission Coatings (MHTC) to minimize false color and is light-baffled with a matte black interior to reduce stray light and reflections, ensuring optimal image contrast.

Figure 1: The Sky-Watcher EvoStar 120 APO Doublet Refractor Telescope, fully assembled.

2. Key Features

• Expertly Matched Glass: Features a matched doublet objective including one synthetic fluorite element for excellent color correction in visual and photographic uses.
• Outstanding Color Correction: Utilizes high-quality glass and proprietary Metallic High-Transmission Coatings (MHTC) for sharp images with accurate color and minimal aberrations.
• Versatile Design: Suitable for both seasoned astrophotographers and novice users, serving as a primary optical tube as skills develop.
• 10:1 Dual-Speed Focuser: A Crayford-style focuser provides precise focusing for various eyepieces and cameras.
• Comprehensive Accessories: Includes a foam-lined aluminum hard case, 8x50 Right Angle Correct Image (RACI) Finderscope, 2" Dielectric Diagonal, 5mm and 25mm LET Eyepieces, 1.25" Adapter, Mounting Rings, and a V-Style Dovetail.

3. Setup

1. Unpacking: Carefully remove all components from the foam-lined aluminum hard case. Inspect for any damage.
2. Mounting the Telescope: Attach the provided mounting rings to a compatible equatorial or alt-azimuth mount. Secure the telescope optical tube within the mounting rings. Ensure the V-style dovetail is properly seated and tightened.
3. Installing the Finderscope: Slide the 8x50 Right Angle Correct Image (RACI) Finderscope into its bracket on the main telescope tube and tighten the retaining screws.
4. Attaching the Diagonal: Insert the 2" dielectric diagonal into the focuser drawtube and secure it with the thumbscrew.
5. Inserting an Eyepiece: Insert either the 25mm or 5mm LET eyepiece into the diagonal. If using 1.25" eyepieces, use the provided 1.25" adapter. Secure the eyepiece with the thumbscrew.
6. Balancing the Telescope: With all accessories attached, adjust the telescope's position within the mounting rings to achieve proper balance on your mount. This prevents strain on the mount and allows for smoother tracking.

Figure 2: Cast aluminum mounting rings and anodized machined dovetail plate for secure mounting.

Figure 3: Included 2" dielectric diagonal and 1.25" eyepieces (25mm and 5mm LET).

4. Operating

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 streetlight during the day). Center the object in the main telescope's eyepiece, then adjust the finderscope's alignment screws until the same object is centered in its crosshairs.
2. Focusing: Use the 10:1 dual-speed Crayford-style focuser to achieve a sharp image. The larger knob provides coarse adjustment, while the smaller knob offers fine adjustment for precise focus.
3. Observing: Begin with the lower magnification 25mm eyepiece for a wider field of view to locate objects. Once an object is found, you can switch to the higher magnification 5mm eyepiece for more detailed views.
4. Minimizing Stray Light: The telescope's internal knife-edge baffles are designed to reduce stray light. Ensure the dew shield is extended during observation to further minimize external light interference and dew formation on the objective lens.

Figure 4: The 2-inch dual-speed Crayford-style focuser for precise image focusing.

5. Maintenance

• Cleaning Optics: Dust on the objective lens should be removed with a soft brush or compressed air. For smudges or fingerprints, use a specialized optical cleaning solution and a microfiber cloth, applying gentle, circular motions from the center outwards. Avoid touching optical surfaces directly.
• Storage: When not in use, store the telescope in its foam-lined aluminum hard case to protect it from dust, moisture, and physical damage. Store in a dry, temperature-stable environment.
• Tube Baffles: The knife-edge baffles within the optical tube are crucial for maintaining image contrast by reducing stray light. Keep the interior of the tube free from dust and debris.

Figure 5: Internal knife-edge baffles designed to reduce stray light and improve image quality.

6. Troubleshooting

• Poor Image Quality / Fuzzy Views:
  • Ensure the focuser is precisely adjusted.
  • Check for atmospheric conditions (e.g., heat haze, turbulence).
  • Verify eyepieces and diagonal are clean and free of dust or smudges.
• Difficulty Finding Objects:
  • Re-align the finderscope with the main telescope.
  • Start with the lowest magnification eyepiece (25mm) for a wider field of view.
• Visible Color Fringing: While the APO design minimizes chromatic aberration, very bright objects (e.g., Venus, bright stars) under certain atmospheric conditions might exhibit minimal color fringing. This is generally within expected performance limits for a doublet refractor.
• Mechanical Instability: Ensure all mounting rings, dovetail clamps, and focuser locking screws are securely tightened. Periodically check the hinge pins on tube rings for secure fitment.

7. Specifications

8. What's in the Box

• Sky-Watcher EvoStar 120 APO Optical Tube
• Foam-lined Aluminum Hard Case
• 8x50 Right Angle Correct Image (RACI) Finderscope with bracket
• 2" Dielectric Diagonal
• 25mm LET Eyepiece (1.25")
• 5mm LET Eyepiece (1.25")
• 1.25" Focuser Adapter
• Tube Mounting Rings
• V-Style Dovetail Plate

9. Warranty and Support

The Sky-Watcher EvoStar 120 APO Doublet Refractor telescope comes with a 2-year warranty. For warranty claims, technical assistance, or any product-related inquiries, please contact Sky-Watcher customer service directly. Retain your proof of purchase for warranty validation.