Askar 91F Flat-Field Astrograph

A 91mm f/6.7 Quadruplet APO with a 44mm Image Circle

The core of the Askar 91F is its self-flattened optical design. Unlike traditional refractors that require a separate, carefully spaced field flattener, this quadruplet system has the correction built in. This eliminates the need to calculate back focus or purchase additional accessories, allowing you to connect your camera and start imaging immediately after achieving focus.

The 44mm image circle is specifically designed to cover full-frame CMOS and DSLR sensors, ensuring sharp, pinpoint stars from the center to the corners of your frame. The inclusion of one ED (Extra-low Dispersion) glass element in the air-spaced objective effectively suppresses chromatic aberration, resulting in high-contrast images with true-to-life color rendition, free of distracting purple fringing around bright stars.

3-inch Rack-and-Pinion Focuser with 360° Rotation

To support heavy full-frame cameras and filter wheels without flexure, the Askar 91F is equipped with a rigid 3-inch dual-speed rack-and-pinion focuser. The 1:10 fine adjustment knob allows for critical focus, while the 30mm of focuser travel accommodates a wide range of accessories. A 360° rotator at the rear of the focuser lets you frame your target perfectly without rotating the entire optical tube.

• Included Adapters: The package comes with a set of photographic adapters, including M54x0.75 and M48x0.75 connections, ensuring compatibility with most popular astronomy cameras and T-rings. The M48 adapter also includes a thread for 2-inch filters.
• Visual Versatility: For visual use, the scope includes standard 2-inch and 1.25-inch adapters, making it a capable instrument for observing star clusters and nebulae, not just for imaging them.

A 3.92kg Lightweight Design with Dual Finder Bases

Engineered for portability, the Askar 91F's main tube weighs just 3.92kg (4.52kg with rings and plate), making it an excellent match for mid-sized equatorial mounts. The retractable dew shield reduces the telescope's length to as little as 513mm for transport and storage. Thoughtful mechanical details enhance usability in the field.

• Dual Finder Mounts: Two finder bases are mounted on either side of the focuser, providing flexible mounting options for a guide scope and a finder scope simultaneously.
• Mounting Hardware: The included 230mm Vixen-style dovetail plate provides a secure connection to your mount and features 1/4" and 3/8" screw holes for direct attachment to a photo tripod for terrestrial viewing.

Askar 91F vs. Triplet APOs: The Advantage of an Integrated Flattener

When comparing the Askar 91F to a traditional triplet apochromat like the William Optics FLT 91, the primary distinction is the optical design philosophy. While both deliver excellent color correction, the triplet design requires an additional, separately purchased field flattener to achieve a flat field for astrophotography.

• Simplicity and Cost: The Askar 91F's integrated flattener means there's no complex back-focus spacing to calculate and no extra accessory to buy. This simplifies the imaging train and reduces overall cost.
• Guaranteed Correction: Because the flattener is part of the objective design, the optical correction is perfectly matched to the telescope, eliminating potential issues with third-party flatteners.
• Trade-offs: A triplet with a separate flattener/reducer can offer multiple focal ratios. The Askar 91F is optimized for its native 609mm focal length, prioritizing out-of-the-box imaging readiness over focal length flexibility.