Apochromatic Refractor Telescope Askar 91F Flat-Field

The Askar 91F is an OTA with an aperture of 91 mm, a focal length of 609 mm and a native focal ratio of F6.7.

The optical design of the Askar 91F features a four-element configuration (three elements at the front and one at the rear), including one piece of ED glass, which can effectively reduce chromatic aberration. The Askar 91F supports 44mm full-frame imaging with great performance of the surrounding star points.

The Askar 91F has a flat field design that allows users to avoid back focus calculation and the purchase of additional flattener. After installing imaging accessories, it can be used directly for shooting after the OTA is in focus. This further reduces cost and increases shooting pleasure.

The Askar 91F strikes a balance between practicality and versatility while achieving lightweight portability through its compact design. The OTA weighs only 3.92 kg, with a gross weight of 4.52 kg (including tube rings and dovetail plate).

The Askar 91F is versatile, allowing for both visual observation and astrophotography. For user convenience, it comes standard with three visual accessories: an 8 mm eyepiece, a 20 mm eyepiece, and a 1.25-inch erector prism.

The 8 mm eyepiece has a 76x magnification and the 20 mm eyepiece has a 30x magnification. The Askar 91F can be used with different eyepieces depending on the objective, and both eyepieces are ideal for birding and landscape viewing.

Both eyepieces measure 1.25 inches and have a soft rubber top for comfortable use.

The 1.25-inch erector prism provides correct left-to-right and bottom-to-top image views, making it easy for users to make terrestrial and astronomical observations without the hassle of viewing inverted top-down, left-to-right images.

The Askar 91F also comes standard with a photographic extension tube with a built-in 2-inch filter thread for easy shooting connections, providing M48×0.75 and M54×0.75 adapters to fit various DSLR cameras and professional astronomical cameras, satisfying diverse imaging needs.

The mechanical design of the Askar 91F adheres to Askar 's consistent philosophy of taking user habits into account and minimizing invisible user costs.

The Askar 91F features a retractable spray shield, further reducing overall length and improving portability. The inside of the tube is bonded with matte felt to better eliminate stray light, while the exterior sports a sleek blue and white color scheme with high-quality CNC machining and paint finish.

The handle of the Askar 91F is 130 mm long and has a groove for the finder base. In addition, it features two finder bases on either side of the focuser, which not only eliminates the need for disassembly when changing the finder position, but also provides additional mounting positions for other astronomical accessories.

In terms of the focuser, the Askar 91F is equipped with a 3-inch dual-speed R&P rigid focuser, which has a 1:10 fine adjustment and a 360° scaled rotator at the rear end for precise angle adjustment. The 230 mm Vixen style dovetail plate includes 1/4" and 3/8" screw holes for direct tripod mounting

The rear interface of the Askar 91F includes 2" and 1.25" adapters, allowing compatibility with a wide range of astronomical accessories.

Whether for deep sky astrophotography, planetary observation, birding and travel, the 91F is your ideal companion for exploring the world.

SPECIFICATIONS

Diameter: 91 mm

Focal length: 609 mm

Focal ratio: f/6.7

Objective Lens: Air-spaced quad APO (including an ED lens)

Imaging circle: 44 mm

Maximum accessory attachment (with focuser fully retracted)

Imaging mode:

75 mm (from the base of the M48×0.75 male thread)

93 mm (from the base of the M54×0.75 male thread)

Observation mode:

112 mm (from the end of the 1.25" eyepiece holder)

122 mm (from the end of the 2" eyepiece holder)

Total length: 513 mm (including 1.25" adapter with spray shield retracted)

599 mm (including 1.25" adapter with spray shield fully retracted)

550 mm (including photo adapter with spray shield retracted)

636 mm (including photo adapter with fully extended spray guard)

Focuser travel length: 3 cm

Net weight: 3.92 kilograms

Gross weight (including tube ring and dovetail plate): 4.52 kilograms (4.52 kilograms)

Rear end thread type: M64×1-M54×0.75 M54×0.75-M54×0.75-M54×0.75-M54×0.75-M48×0.75 (with M48×0.75 filter thread)

Standard package items: OTA 91F, one pair of tube rings, one handle, one 230 mm dovetail plate Vixen, one set of photographic adapters, one 1.25 inch erector prism, one 8 mm eyepiece, one 20 mm eyepiece.