Askar 71F Quadruplet Flat-Field APO f/6.9

Askar 71F: A 71mm Flat-Field APO for Full-Frame Imaging

The Askar 71F combines a 71mm aperture with a 490mm focal length, an f/6.9 system that suits large deep-sky objects like the Andromeda Galaxy (M31) or the North American Nebula (NGC 7000). It is self-flattened, so no separate flattener is needed for its 44mm image circle.

Whether you connect a DSLR or an astronomy camera, it is convenient to use, and its weight and size are controlled to make it easy to carry. It is also designed for visual observation.

Quadruplet APO Optics with 1 ED Element

At the heart of the Askar 71F is a quadruplet air-spaced apochromatic (APO) objective lens. The four-element design includes one ED (Extra-low Dispersion) glass element, which can effectively reduce chromatic aberration.

The 71F supports 44mm full-frame imaging with great performance of the surrounding star points, without additional optical components.

490mm Focal Length at f/6.9

The 490mm focal length positions the Askar 71F squarely in the wide-field imaging category. With a full-frame sensor the field is about 4.2 x 2.8 degrees, wide enough for large emission nebulae and star clusters.

The short 490mm focal length is forgiving of small tracking errors.

A 44mm Corrected Field with No External Flattener

The standout feature of the Askar 71F is its self-flattened design, which produces a 44mm corrected image circle. This is large enough for full-frame sensors (36x24mm), and no separate field flattener is needed.

This lets users avoid calculating the back focus and buying an additional flattener, which reduces cost.

• Full-Frame Ready: The 44mm image circle covers sensors up to 36x24mm.
• No Back Focus Calculation: Simply attach your camera with the included adapters, focus, and start imaging.
• Reduced Complexity: One fewer component in the imaging train.

Adapters, Filters, and Back Focus Simplified

The Askar 71F is designed for immediate use with modern imaging cameras. It ships with a photographic extension tube whose adapters run M64×0.75 to M54×0.75, M54×0.75 to M54×0.75 and M54×0.75 to M48×0.75, with a built-in 2-inch filter thread.

Because the optical system is self-flattened, there is no fixed 55mm requirement. With the focuser fully retracted, the manual gives a maximum accessory connection of 82.5mm from the base of the M48×0.75 male thread (100.5mm from the M54); plan filter drawers and off-axis guiders within it.

2.4-inch Rack & Pinion Focuser with 360° Rotator

The Askar 71F has a dual-speed 2.4-inch rigid rack-and-pinion focuser with 50mm of travel.

It has a 1:10 fine adjustment and a 360° scale field rotator at the rear for precise angle adjustment, with a locking screw. The manual marks screw positions for an electric focusing bracket.

The 0.75x Reducer for f/5.2 Wide-Field Imaging

For imagers seeking an even wider field of view and faster imaging times, Askar offers an optional 0.75x reducer specifically designed for the 71F. This triplet with field flattening gives 369mm at f/5.2; the same exposure takes about 57% of the time needed at f/6.9.

The reducer supports a 44mm full-frame image circle and weighs 0.23kg. Unlike the native system, it needs the standard 55mm back focus from the base of its M48 male thread. Both end threads are M59×1, and the 71F extension tube adapters connect directly to it.

Pairing Cameras and Accessories with the 71F

The Askar 71F's design facilitates easy integration with a complete astrophotography setup. Its 44mm image circle covers full-frame sensors, and smaller APS-C and Micro Four Thirds sensors use its central part.

The M54 and M48 adapters suit astronomy cameras; DSLR or mirrorless cameras use an M48 T-ring. 2-inch filters screw into the adapter's filter thread, or you can add a filter drawer within the connection distance.

3.0kg Portability and Imaging-Focused Design

The lens tube is CNC machined with a blue and white finish. The retractable dew shield, covered inside with matting paint against stray light reflections, brings the length down to 372.5mm (with the 1.25-inch adapter).

The 71F features three separate finder bases: one integrated into the carry handle and two on either side of the focuser. This removes the need for disassembly when moving the finder and adds mounting positions for other accessories. The 230mm standard Vixen-style dovetail plate has slotted 1/4 and 3/8 screw holes for direct tripod attachment.

Weight, Length, and What's in the Box

The optical tube assembly (OTA) alone weighs just 2.5kg. With the included tube rings, carry handle, and 230mm Vixen dovetail plate, the gross weight is 3.0kg.

The telescope's length varies depending on the configuration. For visual use with the dew shield contracted, it measures 372.5mm. For photography with the adapters attached and the dew shield contracted, the length is 415mm. The package includes the OTA, a pair of tube rings, a handle, a 230mm Vixen dovetail plate and a set of photographic adapters.

Getting Started with the Askar 71F

Thanks to its integrated design, setting up the Askar 71F for a night of imaging is straightforward. There are no complex back focus calculations to perform, allowing you to get on target faster.

1. Mount the Telescope: Secure the 230mm Vixen dovetail plate to your equatorial mount.
2. Attach Your Camera: Use the appropriate included adapter (M54 or M48) to connect your astronomy camera or DSLR/mirrorless with its T-ring.
3. Balance the System: With your camera and any other accessories (like a guide scope) attached, adjust the telescope's position in the mount's saddle until it is balanced on both axes.
4. Achieve Focus: Point the telescope at a bright star. Use your camera's live view and a Bahtinov mask to achieve critical focus with the 1:10 fine-focus knob.
5. Frame Your Target: Loosen the rotator's locking screw, rotate your camera to the desired orientation, and then re-tighten the screw. You are now ready to begin your imaging sequence.