Askar 131F Flat-Field APO Refractor

A 131mm f/7.5 Self-Flattening Quadruplet APO

At the heart of the Askar 131F is a quadruplet air-spaced apochromat with four lens elements (three in the front and one in the rear). One of them is ED (Extra-low Dispersion) glass, which can effectively reduce chromatic aberration.

The 131mm aperture gathers light for faint galaxies and nebulae, and the 983mm focal length gives the image scale for medium-sized targets.

44mm Image Circle with No External Flattener

The defining characteristic of the Askar 131F is its "self-flattening" design. Unlike conventional refractors that require a separate field flattener for astrophotography, the 131F is self-flattened: after attaching the imaging accessories, you can shoot directly once the OTA is in focus. There is no separate component to buy, install and space.

It supports 44mm full-frame imaging. The effective connection range is 42mm to 73mm from the base of the M48×0.75 male thread.

3-inch Rack & Pinion Focuser with 30mm of Travel

The Askar 131F is equipped with a 3-inch rack-and-pinion dual-speed focuser with 30mm of travel.

It supports 1:10 fine focusing, and a field rotator marked with 360° scales on the focuser inner tube allows precise framing, with a rotator locking screw.

The 4-Piece Photographic Adapter System

The Askar 131F includes a standard four-section photographic extension tube with a built-in 2-inch filter thread.

The included adapters are:

• M78×1 55mm Extension: The M78 extension adapter.
• M78×1 to M54×0.75 Adapter: Has a built-in reducer mounting thread.
• M54×0.75 to M54×0.75 Adapter: A 13.5mm M54 extension.
• M54×0.75 to M48×0.75 Adapter: A 4.5mm M48 filter adapter ending in a male M48×0.75 thread, with a built-in 2-inch filter thread.

Optional 0.74x Reducer for f/5.6 Wide-Field Imaging

For imagers seeking a wider field of view and shorter exposure times, Askar offers a dedicated 0.74x reducer for the 131F.

When installed, the reducer changes the telescope's specifications as follows:

• Focal Length: Reduces from 983mm to approximately 733.6mm.
• Focal Ratio: Speeds up from f/7.5 to f/5.6.

At f/5.6 the same exposure takes about 56% of the time needed at f/7.5. The reducer is a triplet with field-flattening correction that supports a 44mm full-frame image circle, has a standard 55mm back focus from the base of the M48 male thread, M72×1 threads on both ends and a built-in 2-inch filter thread, and weighs 0.56kg.

9.4kg with Rings, Handle and Dovetail

The optical tube assembly (OTA) alone weighs 7.9kg, and the gross weight comes to 9.4kg with the included tube rings, handle and 300mm Losmandy-style dovetail plate. The tube rings have CNC-machined thumb screws and a clamshell opening for tool-free installation and removal.

Key mechanical features include a retractable dew shield that reduces the telescope's length from 1026mm (photographic extension tube, dew shield extended) to 878mm (1.25-inch adapter, fully retracted). The CNC machined and painted tube includes an internal baffle to suppress stray light. There is a finder base slot on the handle bar and two finder bases on both sides of the focuser, for moving the finder without disassembly and for other accessories.

Imaging Train Integration: Pairing Cameras and Accessories

The 44mm image circle covers full-frame sensors, and the included adapter set ends in a male M48×0.75 thread. With the focuser fully retracted, the connection distance is up to 73mm from the base of this thread (91mm from the M54×0.75), and 42mm with the focuser fully extended.

Askar's example chain fits a 19.5mm off-axis guider, an 18mm filter drawer and an astronomy camera with 17.5mm back focus within this range. The built-in M48×0.75 filter thread on the final adapter allows you to place 2-inch filters at the front of your imaging train.

Visual Observation with the Askar 131F

Askar designs the 131F for visual observation as well as imaging. The rear interface includes 2-inch and 1.25-inch adapters for diagonals and eyepieces. The 131mm aperture gathers enough light to provide bright, high-contrast views of the Moon, planets, and brighter deep-sky objects.

With its 983mm focal length, the telescope can achieve high magnifications for resolving planetary detail, splitting double stars, and exploring globular clusters. For wide-field sweeping, a low-power 2-inch eyepiece will deliver expansive views of open clusters and large nebulae.

First Night Out: A Getting Started Guide for the Askar 131F

Setting up the 131F for your first imaging session is straightforward thanks to its integrated design. First, attach the 300mm Losmandy-style dovetail plate to an equatorial mount rated for the 9.4kg telescope plus your imaging gear. Attach your camera using the provided adapters and add any other accessories like a guide scope.

Balance the telescope carefully in both axes. Power on your mount and camera, then slew to a bright star. Use a Bahtinov mask and the 1:10 fine-focus knob to achieve critical focus. Once focused, you can use the 360-degree rotator to frame your deep-sky target. With the connection inside Askar's 42mm to 73mm range, you are ready to start your imaging sequence. As a critical safety measure, remember to never look at the Sun through the telescope, as it will cause irreversible damage to your eyes.