Askar 91F 91mm f/6.7 Flat-Field Quadruplet APO Refractor

A 91mm flat-field refractor you can carry with one hand, for imaging and observing

The Askar 91F Flat-Field is a 91mm f/6.7 air-spaced quadruplet APO refractor: three elements up front, including one ED element to control color, and one at the rear that flattens the field for full-frame (44mm) sensors. It comes with tube rings, a 130mm handle with a finder base slot, two more finder bases at the focuser, a 230mm Vixen-style plate with 1/4" and 3/8" threaded holes, and photographic adapters with M48 and M54 threads. It's a good first serious imaging refractor, and a sharp grab-and-go scope for the Moon, planets and wide star fields.

Key specs: 91mm aperture · 609mm focal length · f/6.7 · quadruplet air-spaced APO with 1 ED element · 44mm image circle, no flattener needed · 3" rack-and-pinion focuser, 1:10 fine focus, 360° rotator · 4.52kg (10.0lb) with rings, handle and plate

What you can image and see

• Nebulae: the Orion Nebula with the Running Man, the Horsehead and Flame Nebulae, the Rosette Nebula, the Lagoon Nebula, the Eagle Nebula, the Pacman Nebula and the Heart Nebula's core.
• Galaxies: the Triangulum Galaxy (M33), M81 and M82 together, the Leo Triplet and the Whirlpool Galaxy (M51).
• Planetary nebulae and clusters: the Helix Nebula, the Dumbbell Nebula, the Pleiades with their dust, and the Double Cluster.
• At the eyepiece: Saturn's rings, Jupiter's moons and belts, lunar craters, and daytime views: Askar's sample shows 30x with a 20mm eyepiece and 76x with an 8mm.

Fields of view at 609mm: 3.39° × 2.26° with a full-frame sensor (wide enough for the whole Andromeda Galaxy), 2.21° × 1.48° with an APS-C camera such as the ASI2600MC Pro (1.27″ per pixel), and 1.06° × 1.06° with the ASI533MC Pro.

How it works

Imaging: thread the included extension tubes onto the focuser; they end in an M54 × 0.75 or M48 × 0.75 male thread, with a 2" filter thread built in. Spacing isn't critical on this self-flattened design: the sensor can sit anywhere from 45 to 75mm behind the M48 thread (63 to 93mm behind the M54 thread) and still reach focus, so a filter drawer or off-axis guider fits in front of a camera without special spacers.

Visual: use the built-in 2" or 1.25" adapter with a diagonal and eyepiece. A 32mm eyepiece gives about 19x; a 6mm about 100x.

Focusing and framing: the dual-speed rack-and-pinion focuser has a 1:10 fine knob and a 360° scaled rotator. For autofocus, a ZWO EAF replaces the coarse focus knob using a 5 to 6mm flexible coupling, as Askar's assembly diagram shows.

Mounting: the 230mm Vixen-style plate fits most mount saddles, and its 1/4" and 3/8" holes let it sit on a sturdy photo tripod or fluid head for daytime and quick visual use.

What to add for the best results

• A mount (required for imaging): the ZWO AM5N with TC40 tripod carries 15kg (33lb) without a counterweight and leaves room for future telescopes.
• A camera: the ZWO ASI2600MC Air with built-in ASIAIR and guider keeps cables to a minimum; the ASI2600MC Pro or ASI533MC Pro pair with an ASIAIR Plus.
• Guiding: the Askar 32mm f/4 guide scope on one of the finder bases with an ASI120MM Mini or ASI220MM Mini.
• Autofocus: the ZWO EAFN or EAF Pro.
• Filters: a 2" Askar Colour Magic C1 (Hα + OIII) or ZWO Duo-Band filter threads into the extension tube for nebulae from the city.
• For visual use: a 2" diagonal such as the Celestron 2" dielectric star diagonal and eyepieces from our eyepiece collection.
• Field power: the Celestron PowerTank Lithium Pro for dark-site nights away from an outlet.

Askar F-series comparison

All five share the same 44mm full-frame image circle and self-flattened quadruplet design. See all Askar telescopes.

What's in the box

• Askar 91F Flat-Field optical tube with retractable dew shield
• Pair of tube rings with 130mm handle
• 230mm Vixen-style dovetail plate
• Set of photographic adapters (extension tubes with M54 and M48 threads and a 2" filter thread)
• 1.25" and 2" visual adapters

A mount, camera, diagonal, eyepieces and finder are sold separately.

Askar 91F FAQ

Is the 91F good for beginners?

Yes. It's one of the easier imaging refractors to start with: no flattener spacing, a forgiving image scale for guiding, and a weight most mid-size mounts carry easily. It's also a simple, collimation-free visual telescope.

91F or 71F?

The 91F has 64% more aperture area and 609mm of focal length for smaller targets and brighter visual views. The 71F is 1.5kg lighter, 135mm shorter, frames a wider 2.75° × 1.84° on APS-C, and goes on a lighter mount.

91F or 111F?

The 111F reaches 766mm for galaxies but weighs 6.76kg and needs a sturdier mount. The 91F is the better all-rounder if you also want to travel with it.

Can I see Saturn and Jupiter with it?

Yes. Saturn's rings and Jupiter's belts and four bright moons are clear at 100–150x on steady nights.

Do I need a reducer?

No. It's flat-field as is. Askar's 0.75x reducer for the 91F brings it to about 457mm and f/5 if you want a wider, faster field; ask us about availability.

Specifications