Askar 131F Flat-Field APO Refractor

131mm f/7.5 Quadruplet APO: Color-Free, Flat-Field Imaging

The core of the 131F is its advanced quadruplet objective lens. This design uses four air-spaced elements, including one ED (Extra-low Dispersion) glass element, to aggressively suppress chromatic aberration. Unlike standard doublets or triplets, this configuration corrects for color fringing and field curvature across the 44mm image circle, producing pinpoint stars on a dark background without requiring additional corrective optics.

44mm Image Circle: Full-Frame Ready, No Flattener Required

The defining feature of the Askar 131F is its "self-flattening" optical system. This eliminates the most common point of failure and complexity in imaging setups: calculating and achieving the correct back focus for a separate flattener. The 44mm image circle fully illuminates full-frame sensors, and with the included M48 and M54 adapters, you can directly attach your camera, focus, and begin imaging immediately.

• No Additional Purchases: The integrated flattener means you save the cost and weight of a separate optical corrector.
• Zero Back Focus Calculation: Simply attach your camera via the appropriate adapter and use the 30mm of focuser travel to achieve a sharp, flat field.
• Filter Integration: The M54 to M48 adapter includes standard M48x0.75 filter threads, allowing you to easily add 2-inch filters to your imaging train.

9.4kg Gross Weight: Robust Mechanics and 30mm Focuser Travel

Engineered for stability, the Askar 131F weighs 9.4kg when fully assembled with its included tube rings, handle, and 300mm Losmandy-style dovetail plate. The OTA itself has a net weight of 7.9kg and a variable length from 878mm to 1026mm depending on the adapter used and dew shield position. High-quality CNC machining ensures precise alignment, while the robust focuser provides 30mm of travel for fine-tuning focus with a variety of cameras.

Askar 131F vs. Triplet APOs: The Integrated Flattener Advantage

While many high-end refractors use a triplet objective, they almost always require an additional field flattener or reducer/flattener for astrophotography. This introduces complexity, potential tilt, and critical back focus spacing requirements that must be met with precision spacers.

The Askar 131F's quadruplet design incorporates that correction into the main optical tube. This provides a significant advantage: you get a guaranteed flat field optimized for the telescope's native 983mm focal length without any extra components or calculations. While a triplet with a separate flattener might offer more flexibility with reducers, the 131F delivers perfect out-of-the-box performance for full-frame imaging at its designed focal ratio.