Askar FRA400C 72mm f/5.6 Quintuplet APO

Quintuplet Petzval-like APO Optics with 2 ED Elements

The optical system of the FRA400C is a five-element, air-spaced apochromatic (APO) design that includes two Extra-Low Dispersion (ED) glass elements. The ED elements reduce chromatic aberration, the colored halos around bright stars.

The Petzval structure makes the FRA400C "focus-ready": it eliminates the need for back focus calculations, and with a connection distance between 50mm and 60mm you can shoot directly once the OTA is in focus.

72mm Aperture and 400mm Focal Length for Wide-Field Imaging

With a 72mm aperture and a 400mm focal length, the FRA400C operates at a native focal ratio of f/5.6. On a full-frame sensor it covers about 5.1 x 3.4 degrees, enough for the North America Nebula (NGC 7000) with the Pelican, or the Andromeda Galaxy (M31).

The f/5.6 focal ratio strikes a balance between light-gathering speed and optical correction. It collects signal on faint deep-sky objects in a reasonable time.

A 44mm Image Circle with No Flattener Required

The FRA400C supports a 44mm full-frame image circle, large enough to cover a full-frame (36x24mm) sensor.

Because of the Petzval-like structure, you do not need to buy an external flattener or calculate its spacing. Askar supports a connection distance of 50mm to 60mm and recommends 55mm.

A 17-Blade Aperture for Astro and Terrestrial Photography

The FRA400C has an integrated 17-blade aperture that adjusts from f/5.6 to f/22 with an aperture handwheel. Askar marks the scales on the tube for step-based adjustments that prevent accidental changes and preserve settings.

For daily photography, stopping down controls exposure and depth of field. The focus ring is marked with focus distances for quicker focusing, the closest focus distance is 5m, focusing is manual, and the front takes 82mm filters.

Helical Focuser with EAF Compatibility and Rotator

The FRA400C uses a one-speed helical focuser with a locking screw, integrated into the tube. Its adjustable damping structure can be tightened for stability in astrophotography or loosened for faster focusing in daily photography.

For automated focusing, the focuser ring is equipped with an MXL-type synchronous gear. This lets you attach an electronic focuser with an MXL timing belt. The entire OTA can be rotated to adjust angles during imaging, with a rotator locking screw.

M48, M54, and M72 Adapters with 55mm Back Focus

The FRA400C rear end has a four-piece photographic adapter (M72-M54-M48).

• M48 Adapter: M48×0.75 with a built-in 2-inch filter thread.
• Connection distance: Askar supports 50mm to 60mm and recommends 55mm.
• Visual Adapters: For visual use, the telescope includes both 1.25" and 2" eyepiece adapters, for visual observation.

The f/3.9 System with the Optional 0.7x Reducer

Askar makes an optional 0.7x full-frame reducer specially designed for the FRA400C, a triplet weighing 0.46kg.

When attached, the reducer shortens the focal length from 400mm to 280mm and speeds up the focal ratio from f/5.6 to a very fast f/3.9. At f/3.9 the same exposure takes about 48% of the time needed at f/5.6. The reducer provides flat-field correction, supports full-frame imaging, and has a standard 55mm back focus from the base of the M48 male thread with a built-in 2-inch filter thread.

A 2.68kg OTA with a 290mm Vixen Dovetail

Portability is a key design element of the FRA400C. The optical tube assembly (OTA) weighs just 2.68kg, and the total weight with the included tube rings, handle, and dovetail plate is 3.18kg. The total length is 370mm.

The expandable tube ring has four sets of M4 and M6 threaded holes for accessories, and two finder bases are included. A quick-release multifunctional handle sits at the bottom of the tube ring with holes for dovetail plates or equipment, plus M6, 1/4" and 3/8" threads for tripod mounting, and doubles as a carrying grip when the telescope is flipped. A standard 290mm Vixen-style dovetail plate is included.