Askar 91F 91/609 Flatfield

Askar 91F The Askar 91F is a 91mm aperture refractor with a 609mm focal length at f/6.7. Its air-spaced quadruplet uses a front triplet and rear correcting element, including one ED element. The integrated optical design supports a 44 mm full-frame image circle.

Manufacturer model: Askar 91F · Specifications checked against manufacturer data on 2026-11-04

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Askar 91F

The Askar 91F is a 91mm aperture refractor with a 609mm focal length at f/6.7. Its air-spaced quadruplet uses a front triplet and rear correcting element, including one ED element. The integrated optical design supports a 44 mm full-frame image circle.

Native imaging and visual use

Field correction is built into the telescope, so native photography does not need a separate flattener or a single mandatory flattener spacing. Attach the camera within the connection limits and focus. The table gives maximum and minimum connection distances for each rear adapter and focuser position. The 2-inch and 1.25-inch visual interfaces also accommodate observing accessories.

Focus, framing and filters

The 3-inch rack-and-pinion focuser provides coarse and 1:10 fine adjustment, plus a graduated 360° rotator. The photographic extension assembly offers M54×0.75 and M48×0.75 connections and an internal 2-inch filter thread.

Mounting and transport

Two finder bases and a finder-base slot in the handle provide accessory positions. The telescope includes tube rings and a 230 mm Vixen-style dovetail plate. Its retractable dew shield shortens the transport configuration. Lengths and weights below distinguish the visual and photographic arrangements and the bare OTA from mounting hardware.

Askar manufacturer documentation

Compatibility notes

Exact named-model manufacturer specification table and operating information checked. Unpublished values are not inferred.

Referencia 90697

Ficha técnica

Aperture: 91mm
Dew shield: Retractable
Dovetail: 230 mm Vixen-style
Field correction: Integrated 3+1 optical system; no separate native flattener
Filter thread: M48×0.75, 2-inch
Finder bases: 2
Fine focus ratio: 1:10
Focal length: 609mm
Focal ratio: f/6.7
Focuser: 3-inch dual-speed rack-and-pinion
Focuser travel: 30mm
Handle: Finder-base slot
Image circle: 44mm
Length configurations: 513mm(including 1.25" adapter as dew shield contracted） 599mm(including 1.25" adapter as dew shield fully stretched） 550mm(including the photographic adapter as dew shield contracted） 636mm(including the photographic adapter as dew shield fully stretched）
Manufacturer standard package: A 91F OTA，a pair of tube rings, a handle, a 230mm Vixen dovetail plate,a set of photographic adapters
Maximum accessory connection focuser retracted: Imaging mode: 75mm (from the base of M48×0.75 male thread） 93mm（from the base of M54×0.75 male thread); Observing mode: 112mm（from the end of 1.25" eyepiece holder） 122mm（from the end of 2" eyepiece holder）
Minimum accessory connection focuser extended: Imaging mode: 45mm (from the base of M48×0.75 male thread） 63mm（from the base of M54×0.75 male thread); Observing mode: 82mm（from the end of 1.25" eyepiece holder） 92mm（from the end of 2" eyepiece holder）
Model: 91F
Optical design: Quadruplet air-spaced APO(including one ED glass)
OTA weight: 3.92kg
Rear thread interfaces: M64×1-M54×0.75 M54×0.75-M54×0.75 M54×0.75-M48×0.75 (with M48×0.75 filter thread)
Rotator: 360° graduated
Weight with rings and dovetail: 4.52kg

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