Askar 91F – 91/609 mm f/6.7 Flat-Field Quadruplet Apochromatic Refractor

The Askar 91F is a flat-field quadruplet apochromatic refractor, designed to offer a complete optical system that is ready to use for both deep-sky astrophotography and visual observation. It features a 91 mm aperture, a 609 mm focal length, and a native focal ratio of f/6.7.

The optical design consists of four elements—three front elements and a rear corrector—and includes an ED (extra-low dispersion) glass element to effectively limit chromatic aberration, resulting in sharp, high-contrast, and detailed images.

Thanks to the integrated field corrector, the Askar 91F provides a 44 mm corrected image circle, which is also suitable for cameras with full-frame sensors. There is no need to purchase a separate flattener or maintain a specific photographic backfocus: simply attach your camera, reach focus, and start capturing.

Flat-Field Quadruplet Optics

• Four-element apochromatic optical design
• Three front elements and an integrated rear corrector
• ED optical element for superior chromatic correction
• Flat field with no need for an additional flattener
• 44 mm corrected image circle
• Compatible with full-frame astronomical and photographic cameras
• No specific photographic backfocus distance to calculate

Precise and Versatile Mechanics

The telescope is equipped with a sturdy 3" Rack & Pinion focuser, featuring a 1:10 fine-adjustment micro-focuser and a 30 mm travel distance. The 360° rear rotator with a graduated scale allows you to precisely orient the camera and easily select your desired framing.

The retractable dew shield makes the tube more compact during transport, while the matte internal coating helps reduce reflections and stray light. The 130 mm top handle includes a finder shoe, supplemented by additional mounting points on the sides of the focuser for finders, guide scopes, and other accessories.

• 3" Rack & Pinion focuser
• 1:10 dual-speed micro-adjustment
• 360° camera rotator with graduated scale
• Retractable dew shield
• Top handle with finder shoe
• Additional side bases for mounting accessories
• CNC-machined rings
• 230 mm Vixen dovetail bar
• 1/4" and 3/8" threaded holes for tripod attachment

Photographic and Visual Connections

The Askar 91F comes with threaded M54×0.75 and M48×0.75 photographic adapters. The M48 adapter also features a thread for 2" astronomical filters. For visual use, connections compatible with 2" and 1.25" accessories are available.

Technical Specifications

Package contents

• Askar 91F optical tube
• Pair of support rings
• Top handle
• 230 mm Vixen dovetail bar
• Set of photographic adapters