1. Introduction
The Askar FRA600/5.6 is an advanced Quintuplet Petzval Flat-Field Astrograph designed for high-performance astrophotography and observation. It features a 108mm aperture and a 600mm focal length, maintaining an f/5.6 focal ratio. This evolution in the Askar FRA series is engineered to deliver a 66mm image circle, ensuring excellent star shape across a flat field while effectively controlling chromatic aberration and minimizing distortion.
Its optical design incorporates a front triplet and a rear doublet lens, constructed with 5 elements, including two ED (Extra-low Dispersion) elements. The two lenses in the rear group have an 80mm diameter, which significantly reduces the occurrence of decreased field illumination. Precision lens manufacturing ensures theoretical optimal pinpoint stars, resulting in beautifully round stars and clean, detailed images.
2. Setup
2.1 Unpacking and Initial Inspection
Carefully unpack all components. Verify that all listed accessories are present:
- Askar FRA600 Astrograph OTA
- A pair of tube rings
- Handle
- Dovetail plate
- Sectional conical tube adapter (with M54x0.75 and M48x0.75 male thread)
- Inspection list
- User manual (this document)
2.2 Mounting the Astrograph
- Attach the provided tube rings to the main optical tube assembly (OTA).
- Secure the handle to the top of the tube rings.
- Mount the dovetail plate to the bottom of the tube rings. This plate allows you to attach the astrograph to a compatible equatorial mount.
- Ensure all screws are tightened securely but do not overtighten.
2.3 Focuser and Accessory Connection
The FRA600 is equipped with a large 4.2" rack and pinion focuser, featuring a 1:10 micro-adjustment knob for precise focusing. The focuser supports multiple connection threads for various photography equipment.
- Back-end Adapters: The astrograph includes M108x1 male thread (no rotator), M90x1 male thread, 2" adapter, and 1.25" adapter.
- Conical Adapters: A standard conical extension tube is provided with M54x0.75 and M48x0.85 threads for connecting cameras and other accessories.
2.4 Motor Focus Bracket Installation Points
The focuser assembly includes designated points for installing a motor focus bracket, allowing for automated and precise focusing.
1, 3, 4, 5, 7: Motor focus bracket installation points
2: Bottom locking screw hole
6: Bottom carrying capacity adjustment screw hole (with M4 small screw inside)
2.5 Attaching a Camera
Connect your camera to the focuser using the appropriate adapters. Ensure the camera is securely attached to prevent movement during long exposures. The focuser is designed to handle heavy imaging equipment without slipping.
3. Operating the Astrograph
3.1 Astrophotography
The FRA600 is optimized for wide-field astrophotography. Its flat-field design and excellent optical correction ensure sharp stars across the entire image frame. Use the 1:10 micro-adjustment knob for fine-tuning focus to achieve critical sharpness for imaging.
3.2 Visual Observation
While primarily an astrograph, the FRA600 is also suitable for high-quality visual observation. Its apochromatic design provides a complete lack of chromatic aberration, delivering impressive contrast and realistic visual experiences. Attach a diagonal and eyepiece to the focuser for visual use.
3.3 Dew Shield
The astrograph features a retractable dew shield. Extend the dew shield during use to minimize dew formation on the objective lens and to block stray light, improving contrast. Retract it for compact storage and transport.
4. Maintenance
4.1 Cleaning the Optics
The optical surfaces of the FRA600 are delicate. Only clean them when absolutely necessary. Use a soft brush or compressed air to remove loose dust. For smudges or fingerprints, use a specialized optical cleaning solution and a clean microfiber cloth, applying gentle pressure in a circular motion from the center outwards. Never touch the lens surfaces with bare hands.
4.2 General Care and Storage
- Keep the astrograph covered with dust caps when not in use.
- Store the instrument in a dry, dust-free environment, preferably in its original packaging or a padded case.
- Avoid exposing the astrograph to extreme temperatures or sudden temperature changes.
- Regularly check all screws and connections for tightness.
5. Troubleshooting
5.1 Image Quality Issues
- Chromatic Aberration: The FRA600 is designed to minimize chromatic aberration. If colored fringes are observed, ensure proper focus and check for any external factors like atmospheric conditions.
- Distortion: The flat-field design minimizes distortion. If distortion is apparent, verify that all optical components are correctly seated and aligned.
- Decreased Field Illumination: The 80mm rear lenses reduce this effect. If illumination drops off towards the edges of the image, ensure your camera sensor size is compatible with the 66mm image circle and check for vignetting caused by adapters or filters.
- Poor Star Shapes: Ensure precise focus using the micro-adjustment knob. Check for proper collimation (though refractors are generally robust in this regard) and stable mounting.
5.2 Focuser Slipping
If the focuser slips under the weight of heavy imaging equipment, ensure the focuser locking screw is adequately tightened. The 4.2" rack and pinion focuser is designed for high payload capacity, but proper adjustment is crucial.
5.3 General Issues
If you encounter any problems not covered here, or if troubleshooting steps do not resolve the issue, please refer to the Warranty/Support section for assistance.
6. Specifications
The following table details the technical specifications of the Askar FRA600 Astrograph:
| Feature | Specification |
|---|---|
| Aperture | 108mm |
| Focal Length | 600mm |
| Focal Ratio | F5.6 |
| Objective Type | Quintuplet flat-field APO (including two ED elements) |
| Image Circle | 66mm |
| Back Focus | 160mm (from the end of rotator M90x1 thread) |
| Overall Length | 493mm (dew shield retracted) |
| Tube Weight | 6.5kg |
| Standard Packing Weight | 7.8kg |
| Back-end Adapter | M108x1 male thread (no rotator), M90x1 male thread, 2" adapter/ 1.25" adapter |
| Conical Adapter | M90x1 to M54x0.75, M54x0.75 to M48x 0.75 |
| Lens Type | Refractive |
| Type | Monocular |
| Certification | CE |
7. User Tips
- Critical Focus: For astrophotography, achieving critical focus is paramount. Utilize the 1:10 micro-adjustment knob on the focuser for precise adjustments. Consider using a Bahtinov mask for visual focusing or a motor focuser for automated, highly accurate focusing.
- Cable Management: When attaching cameras and other accessories, manage cables carefully to prevent snagging or putting strain on the focuser, which could lead to star trailing or focus shifts during long exposures.
- Balance: Ensure your astrograph and attached equipment are well-balanced on your mount. This is crucial for smooth tracking and to prevent undue stress on the mount's motors.
8. Warranty and Support
For any issues or concerns regarding your Askar FRA600 Astrograph, please contact the seller or manufacturer's support channel. If you find any problem with the product, describe the problem in detail, and support will be provided to help resolve the issue.
