The Askar 91F Flat-Field 91 mm 91/609 f/6.7 Quadruplet air-spaced APO telescope is an apochromatic refractor designed for deep-sky astrophotography and visual observation of the Moon, planets and terrestrial objects. The four-element air-spaced optical system includes one extra-low dispersion (ED) glass element to reduce chromatic aberration. Built-in field correction eliminates the need for an additional flattener, while the 44 mm image circle allows use with full-frame sensors.
The 3" rack & pinion focuser with 1:10 fine adjustment makes precise focusing easier. The 360° rotator with a graduated scale allows adjustment of the framing orientation. The tube features a retractable dew shield and two finder shoes, while the included tube rings, carrying handle and Vixen dovetail bar make the instrument easier to mount and carry.
• four-element apochromatic optical system with an ED element to reduce chromatic aberration
• built-in field correction without the need for an additional flattener
• image circle suitable for full-frame sensors
• rack & pinion focuser with coarse and fine adjustment, plus a rotator for easier framing
• two shoes for attaching a finder or accessories
• retractable dew shield to reduce dew formation and the effects of stray light
• suitable for astrophotography, astronomical observation and nature observation
• Askar 91F Flat-Field 91 mm 91/609 f/6.7 optical tube assembly
• tube rings with a carrying handle
• 230 mm Vixen dovetail bar
• set of photographic adapters: M64 × 1 – M54 × 0.75, M54 × 0.75 – M54 × 0.75 and M54 × 0.75 – M48 × 0.75 with a filter thread
• documentation
• optical design: apochromatic refractor
• lens configuration: air-spaced quadruplet
• number of extra-low dispersion (ED) glass elements: 1
• aperture: 91 mm
• focal length: 609 mm
• focal ratio: f/6.7
• image circle diameter: 44 mm
• full-frame sensor compatibility: yes
• maximum working distance for astrophotography, measured from the base of the M48 × 0.75 thread: 75 mm
• maximum working distance for astrophotography, measured from the base of the M54 × 0.75 thread: 93 mm
• maximum working distance for visual observation, measured from the end of the 1.25" eyepiece holder: 112 mm
• maximum working distance for visual observation, measured from the end of the 2" eyepiece holder: 122 mm
• compatible eyepiece and diagonal barrel diameters: 1.25" and 2"
• filter mounting: M48 × 0.75 thread in the photographic adapter
• focuser diameter: 3"
• focuser type: rack & pinion with coarse adjustment and 1:10 fine adjustment
• rotator: 360° with a graduated scale
• mount attachment: 230 mm Vixen dovetail bar with 1/4" and 3/8" holes
• tube length with the dew shield retracted and the 1.25" adapter: 513 mm
• tube length with the dew shield extended and the 1.25" adapter: 599 mm
• tube length with the dew shield retracted and the photographic adapter: 550 mm
• tube length with the dew shield extended and the photographic adapter: 636 mm
• tube weight without accessories: 3.92 kg
• tube weight with rings and dovetail bar: 4.52 kg
The corrected image field, precise focuser and compatibility with 1.25" and 2" accessories make it easier to configure the telescope for astrophotography or visual observation.
