Askar 91F – Flatfield APO Quadruplet 91 mm f/6.7
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Vai al moduloAskar 91F – Flatfield APO Quadruplet 91 mm f/6.7
The Askar 91F is a four-element apochromatic refractor with ED glass, designed for demanding astrophotographers and visual observers. Its integrated flatfield optical system produces a naturally corrected image plane, eliminating the need for an external field flattener. Stars remain sharp across full-frame sensors without aberration or field curvature.
Flatfield Optics for Full-Frame Cameras
The air-spaced quadruplet design with an ED element effectively suppresses chromatic aberration and field curvature. The fully illuminated 44 mm image circle makes the 91F ideal for full-frame imaging, ensuring uniform sharpness across the entire field.
Precision Mechanics and Compact Design
The optical tube features a retractable dew shield, a fully blackened interior, and high-precision CNC construction. The 3" rack-and-pinion focuser with 1:10 fine adjustment and a 360° rotator enables accurate focusing and precise camera framing. Its compact size and low weight make it easy to transport and operate in the field.
Versatile Applications
The Askar 91F is suitable for deep-sky astrophotography, lunar and planetary observation, as well as terrestrial use such as birdwatching and landscape viewing. Its apochromatic ED optics and solid mechanical performance make it an excellent choice for advanced beginners and experienced astrophotographers.
Technical Specifications
| Specification | Value |
|---|---|
| Aperture | 91 mm |
| Focal Length | 609 mm |
| Focal Ratio | f/6.7 |
| Optical Design | Air-spaced quadruplet with ED glass |
| Flatfield | Native corrected image plane |
| Image Circle | 44 mm |
| Thread Compatibility | M64, M54, M48 with 2" filter thread |
| Focuser | 3" rack-and-pinion, 1:10 fine focus, 360° rotator |
| Net Weight | 3.92 kg |
| Total Weight | 4.52 kg (with rings and dovetail) |
| Telescope Length | 513–636 mm (depending on configuration) |
Included Accessories
- Askar 91F optical tube
- Tube rings with carrying handle
- 230 mm Vixen-style dovetail plate
- Adapter set (M64, M54, M48 with 2" filter thread)
- 1.25" 45° erecting prism
- 1.25" eyepieces: 20 mm (30×) and 8 mm (76×)
- Modular photographic extension tube (4 sections)
- Dual finder shoes on both sides of the focuser
Recommended Uses
- Deep-sky astrophotography with full-frame cameras
- Lunar and planetary observation
- Terrestrial observation (birdwatching, landscapes)
- Ideal for users seeking high optical performance without technical complexity
Key Strengths
- Integrated flatfield design – no external flattener required
- Native support for full-frame sensors (44 mm)
- APO ED optics for high-contrast, high-resolution imaging
- Strong, compact mechanical construction
- Suitable for advanced beginners and experienced astrophotographers