Askar Refractor 91F Flat Field

Askar Refractor 91F Flat Field

Description

The Askar 91F features a quadruplet APO optical structure with three front elements and one rear element, including one ED glass element for effective chromatic aberration reduction. It has a 91 mm aperture, a 609 mm focal length and a native f/6.7 focal ratio. It supports a 44 mm full-frame image circle with excellent edge-of-field star performance.
Its integrated flat-field design eliminates the need for an additional flattener and avoids back-focus calculations. Once imaging accessories are attached and focus is achieved, the OTA is ready for shooting immediately, simplifying the workflow and reducing costs.
Weighing 3.92 kg (4.52 kg including rings and dovetail), the 91F provides a balance of portability and performance. It is suitable for both visual observation and astrophotography and includes three visual accessories: an 8 mm eyepiece, a 20 mm eyepiece and a 1.25" erecting prism. The eyepieces provide 76× and 30× magnifications and include rubber eye guards.
The photographic extension tube includes a 2-inch filter thread and both M48×0.75 and M54×0.75 adapters to support DSLR and astronomy cameras.
The retractable dew shield reduces overall length, while internal matting felt minimizes stray light. The blue-and-white CNC-machined tube ensures a refined appearance.
The 130 mm handle includes a finder slot, and two additional finder bases are positioned on both sides of the focuser.
The 3-inch dual-speed rack-and-pinion focuser offers 1:10 fine adjustment and a 360° scale rotator for precise angle framing. The 230 mm Vixen dovetail plate includes 1/4" and 3/8" threaded holes for direct tripod mounting.
The Askar 91F is suitable for deep-sky astrophotography, planetary observing and terrestrial use.

Technical specifications

• Aperture size: 91 mm

• Focal length: 609 mm

• Focal ratio: f/6.7

• Objective lens: Quadruplet air-spaced APO (one ED glass)

• Image circle: 44 mm

• Maximum accessory connection (focuser retracted):

  • Imaging: 75 mm (M48×0.75), 93 mm (M54×0.75)

  • Visual: 112 mm (1.25"), 122 mm (2")

• Minimum accessory connection (focuser extended):

  • Imaging: 45 mm (M48×0.75), 63 mm (M54×0.75)

  • Visual: 82 mm (1.25"), 92 mm (2")

• Total length:

  • 513 mm (dew shield retracted with 1.25" adapter)

  • 599 mm (dew shield extended with 1.25" adapter)

  • 550 mm (dew shield retracted with photographic adapter)

  • 636 mm (dew shield extended with photographic adapter)

• Focuser travel: 30 mm

• Net weight: 3.92 kg

• Gross weight: 4.52 kg

• Rear thread type: M64×1–M54×0.75 / M54×0.75–M54×0.75 / M54×0.75–M48×0.75 (with M48×0.75 filter thread)

• Standard package: 91F OTA, tube rings, handle, 230 mm Vixen dovetail plate, photographic adapters, 1.25" erecting prism, 8 mm and 20 mm eyepieces