Askar 91F Flat-Field Quadruplet Astrograph Telescope

Askar 91F Flat-Field Quadruplet Astrograph Telescope

The Askar 91F is an optical tube assembly featuring a 91mm aperture, a 609mm focal length, and a native focal ratio of F6.7.

Its optical layout consists of a four-element system – three elements at the front and one at the rear – which incorporates an ED glass element to effectively minimize chromatic aberration. The Askar 91F supports 44mm full-frame imaging and delivers excellent star performance across the entire field.

With its built-in self-flattening design, the Askar 91F eliminates the need to calculate back focus or purchase additional flatteners. Once imaging accessories are connected and the OTA is brought into focus, users can begin shooting immediately. This design reduces overall cost and enhances the ease and enjoyment of astrophotography.

                             ASTROPHOTOGRAPHY                                                      DAILY PHOTOGRAPHY                                                    VISUAL OBSERVATION                             

The Askar 91F achieves an ideal blend of portability, practicality, and versatility through its compact structure. The OTA weighs just 3.92kg, while the total weight – including tube rings and dovetail plate-comes to 4.52kg.

Designed for both visual observing and imaging, the Askar 91F includes three standard visual accessories for user convenience: an 8mm eyepiece, a 20mm eyepiece, and a 1.25-inch erecting prism.

The 8mm eyepiece provides 76× magnification, while the 20mm eyepiece offers 30× magnification. Users can select different eyepieces depending on their observing target, and both eyepieces work exceptionally well for terrestrial viewing such as birds or scenery.

Each eyepiece uses a 1.25-inch barrel and includes a soft rubberized eye guard for comfortable viewing.

The included 1.25-inch erecting prism delivers an upright, correctly oriented image – left-to-right and up-to-down – allowing easy terrestrial and astronomical use without the confusion of reversed images.

Additionally, the Askar 91F is supplied with a photographic extension tube equipped with a built-in 2-inch filter thread for streamlined imaging connections. It also includes M48×0.75 and M54×0.75 adapters, making it compatible with various DSLR and dedicated astronomy cameras to meet different imaging requirements.

The mechanical construction of the Askar 91F follows Askar’s long-standing design philosophy, focusing on user-friendly operation while reducing hidden or unexpected costs.

The Askar 91F comes with a retractable dew shield, helping to shorten the overall length and improve portability. The interior of the optical tube is lined with matte felt to effectively suppress stray light, while the outside showcases a refined blue-and-white finish crafted through precision CNC machining and high-quality paintwork.

The 91F includes a 130mm handle equipped with a finder base slot. Additionally, two finder bases are positioned on either side of the focuser, eliminating the need to remove parts when relocating the finder and offering extra spots for attaching more astronomical accessories.

For focusing, the Askar 91F uses a robust 3-inch rack-and-pinion dual-speed focuser with 1:10 fine adjustment. A 360° engraved rotator at the rear enables accurate angle alignment. The 230mm Vixen-style dovetail plate provides both 1/4" and 3/8" screw holes for direct attachment to a tripod.

The rear interface features adapters for both 2-inch and 1.25-inch accessories, ensuring broad compatibility with various astronomy equipment.

Whether you're capturing deep-sky objects, studying planets, or enjoying terrestrial viewing such as birdwatching or travel, the Askar 91F serves as a reliable and versatile companion for all your adventures.

Product Size Diagram

91F Connection Diagram

The Locking Screw Position Diagram

Electronic Focuser Assembly Diagram

Optical Path Diagram

Spot Diagram