Askar Apochromatic refractor AP 91/609 91F Flatfield (90697)

Askar AP 91/609 Flatfield Apochromatic Refractor OTA (90697)

The Askar AP 91/609 Flatfield is a compact, portable, and high-performance apochromatic refractor designed for astrophotography and visual observation. Combining premium optics with an integrated field flattener, this telescope offers a simple imaging workflow while delivering exceptional image quality across a full-frame sensor.

Its lightweight construction makes it an excellent travel telescope for experienced astrophotographers, while its user-friendly design allows enthusiasts to begin deep-sky imaging without the complexity of separate field flatteners or back-focus calculations.

The telescope is equally well suited for observing the Moon, planets, star clusters, nebulae, galaxies, and terrestrial subjects.

Key features

• 91 mm apochromatic triplet refractor.

• 609 mm focal length.

• f/6.7 focal ratio.

• Integrated field flattener.

• Fully corrected 44 mm image circle.

• ED glass objective.

• Optimized for full-frame cameras.

• Precision rack-and-pinion focuser.

• Dual-speed 1:10 fine focusing.

• Integrated 360° camera rotator.

• Retractable dew shield.

• Compatible with optional electronic focus motors.

• Lightweight and travel-friendly design.

Premium flat-field optical system

The telescope features a sophisticated optical design consisting of a triplet objective combined with a rear correction lens.

The ED glass element effectively minimizes chromatic aberration while maintaining excellent contrast and sharpness across the entire image field.

The integrated field flattener produces a fully corrected 44 mm image circle, making the telescope ideal for full-frame DSLR and astronomical cameras without requiring an additional field flattener.

Simply attach the camera, achieve focus, and begin imaging without complex back-focus adjustments.

Designed for astrophotography

The AP 91/609 has been developed primarily for astronomical imaging while remaining an excellent visual telescope.

Integrated camera connections include:

• M48 × 0.75 thread.

• M54 × 0.75 thread.

• M64 thread.

• Integrated 2-inch filter thread.

These connections provide compatibility with a wide range of DSLR cameras, dedicated astronomy cameras, and imaging accessories.

Compact travel design

The telescope features a retractable dew shield that significantly reduces the transport length for convenient travel.

Additional design features include:

• Precision CNC-machined components.

• Durable high-quality finish.

• Elegant blue and white exterior.

• Matte felt-lined interior to suppress stray light and improve image contrast.

Two finder shoe bases and an integrated carrying handle provide flexible mounting options for accessories.

The supplied 230 mm Vixen-style dovetail rail includes both 1/4-inch and 3/8-inch tripod threads, allowing installation on astronomical mounts as well as photographic tripods.

Precision dual-speed focuser

The telescope is equipped with a premium rack-and-pinion focuser featuring:

• 2-inch accessory connection.

• 1:10 dual-speed fine focusing.

• Precision non-slip focusing knobs.

• 360° camera rotator.

• Locking mechanism.

• Compatibility with optional electronic focus motors, including systems such as the ZWO EAF.

The large 61 mm clear aperture ensures excellent illumination for modern imaging sensors.

Visual observing

Although optimized for astrophotography, the telescope also performs exceptionally well for visual observation.

Its apochromatic optics provide sharp, high-contrast views of:

• The Moon.

• The planets.

• Bright nebulae.

• Open and globular star clusters.

• Galaxies.

• Terrestrial subjects.

Solar observation is possible only when using a properly certified full-aperture solar filter.

Included accessories

• 20 mm 1.25-inch eyepiece.

• 8 mm 1.25-inch eyepiece.

• Retractable dew shield.

• 1.25-inch 45° Amici prism.

• Integrated field flattener.

• Vixen-style dovetail rail.

• 1/4-inch and 3/8-inch tripod mounting threads.

• Carrying handle.

• Vixen/Sky-Watcher finder shoe.

• 2-inch to 1.25-inch eyepiece adapter.

• Tube rings.

Technical specifications

Optical system

• Optical design:

  • Apochromatic refractor.

• Objective design:

  • Triplet with integrated field flattener.

• Aperture:

  • 91 mm.

• Focal length:

  • 609 mm.

• Focal ratio:

  • f/6.7.

• Resolving power:

  • 1.52 arcseconds.

• Limiting magnitude:

  • 11.6.

• Light-gathering power:

  • 170×.

• Maximum useful magnification:

  • 182×.

• Fully corrected image circle:

  • 44 mm.

Optical tube

• Tube weight:

  • 4.52 kg.

• Tube diameter:

  • 96 mm.

• Dew shield diameter:

  • 114 mm.

• Transport length:

  • 513 mm.

Focuser

• Type:

  • Rack-and-pinion.

• Eyepiece connection:

  • 2 inches.

• Camera threads:

  • M48 × 0.75, M54 × 0.75, M64.

• Clear aperture:

  • 61 mm.

• Motorization:

  • Optional.

• Compression ring:

  • Yes.

• Fine-focus reduction:

  • 1:10.

• Focusing travel:

  • 30 mm.

• Rotator:

  • 360°.

• Integrated filter thread:

  • Yes.

• Tilt adjustment:

  • No.

Mounting

• Configuration:

  • Optical tube assembly (OTA).

• Mount included:

  • No.

• Dovetail:

  • Vixen-style.

• Tripod threads:

  • 1/4-inch and 3/8-inch.

Applications

• Astrophotography:

  • Excellent.

• Moon and planetary observation:

  • Yes.

• Deep-sky observation:

  • Yes.

• Nature observation:

  • Yes.

• Solar observation:

  • Only with an appropriate certified solar filter.

Recommended user level

• Beginners:

  • Not primarily intended.

• Advanced users:

  • Yes.

• Permanent observatories:

  • No.