Askar FRA400 72mm f/5.6 Quintuplet APO

The Askar FRA400: A Portable 72mm Full-Frame Astrograph

FRA stands for "Flat-field Refractive Astrograph": a refractor with built-in flat field correction. The FRA400 is the pioneering model of the series and has been a bestseller since its launch.

Askar adds that the FRA can also be applied in visual observation. The included 1.25" and 2" adapters take standard diagonals and eyepieces for wide views of star clusters and nebulae.

Quintuplet APO Optics: A 44mm Flat Field with Two ED Elements

The optical core of the FRA400 is a five-element (quintuplet) Petzval-like design that is fully air-spaced. Two of the five elements are special extra-low dispersion (ED) glass, and the design is excellent in controlling chromatic aberration.

The FRA400's quintuplet layout has built-in field correction, so there is no separate flattener and no back focus to calculate: users only need to achieve focus when shooting.

400mm Focal Length at f/5.6: Framing the Largest Nebulae

The combination of a 400mm focal length and 72mm aperture results in a native focal ratio of f/5.6. With a full-frame sensor the field is about 5.1 x 3.4 degrees, enough to frame the Andromeda Galaxy (M31), the North American Nebula (NGC 7000) or the Veil Nebula complex.

f/5.6 is a relatively fast focal ratio for astrophotography.

The 44mm Image Circle: Full-Frame Coverage, No Flattener Needed

The FRA400 supports a 44mm full-frame image circle, larger than the roughly 43.3mm diagonal of a full-frame sensor.

The key benefit of the FRA series is built-in field correction.

• No Additional Flattener: You do not need to purchase, install, or space a separate field flattener, which simplifies your imaging train.
• Simplified Setup: Users don't need to worry about calculating back focus, as long as the object is focused.

140mm Back Focus from the M68x1 Thread

The FRA400's back focus is 140mm, measured from the end of the rotator's M68x1 male thread to the focal plane.

Your imaging train, such as an off-axis guider, a filter drawer and the camera, sits within that distance. Askar includes an M68-M48 conical adapter, a 2" adapter and a 1.25" adapter.

3" Rack-and-Pinion Focuser: Precision Control and 360° Framing

The FRA400 is equipped with a 3-inch rack-and-pinion focuser with a 360-degree rotator and an M68×1 thread.

Its features:

• 1:10 Fine Adjustment: For more precise calibration in observation or imaging.
• 360° Rotator: A built-in rotator lets you frame your target at any angle.

Optional 0.7x Reducer: f/3.9

For imagers seeking an even wider field of view and shorter exposure times, Askar offers the dedicated F3.9 Full Frame Reducer for the FRA400. This optional 0.7x reducer turns the telescope into a 280mm f/3.9 astrograph; at f/3.9 the same exposure takes about 49% of the time needed at f/5.6.

The reducer has 3 air-spaced elements, a 44mm image circle, a 72mm maximum outer diameter and a standard 55mm back focus. It has a built-in M48×0.75 thread for 2-inch filters.

Pairing the FRA400 with Your Camera and Accessories

The FRA400 works with DSLRs, mirrorless bodies and dedicated astronomy cameras up to full frame, connected through the included M68-M48 conical adapter.

A typical full-frame imaging train might consist of your camera, an off-axis guider for precise tracking, and a filter drawer for narrowband or LRGB filters. This stack is built within the 140mm from the rotator's M68x1 male thread, and the included M68-M48 adapter steps down to M48.

Mechanical Design: Tube, Rings, and Mounting Hardware

The FRA400 is built with portability and functionality in mind. The optical tube has a retractable dew shield (lens hood).

It comes with a pair of multifunctional patented tube rings, with attachments available on three sides of the rings. A multi-functional handle sits on top of the rings and a dovetail plate on the bottom.

Weight, Dimensions, and What's in the Box

The optical tube assembly (OTA) alone weighs only 2.56kg (5.6 lbs). With the included tube rings, handle, and dovetail plate, the total weight is 2.88kg (6.3 lbs).

Its overall length is 317mm. The package includes the FRA400 OTA, a pair of tube rings, a handle, a dovetail plate and an M68-M48 conical adapter.

Your First Night Out with the Askar FRA400

Getting started with the FRA400 is straightforward thanks to its integrated design. After mounting the telescope to your equatorial mount, attach your camera using the appropriate adapters. Build your imaging train within the 140mm from the rotator's M68x1 thread.

Balance the setup in both Right Ascension and Declination. Once aligned, point to a bright star and use a Bahtinov mask to achieve critical focus with the 1:10 fine-focus knob. Use the 360° rotator to frame your target perfectly, lock everything down, and you are ready to begin capturing images.