Askar 151PHQ f/7 Quadruplet Astrograph

A 151mm f/7 Quadruplet APO with 2 ED Elements

The core of the 151PHQ is its air-spaced quadruplet objective lens, which incorporates two extra-low dispersion (ED) glass elements. The quadruplet with two ED glasses offers excellent control of chromatic and other aberrations, with a central RMS radius of less than 2 microns.

At an aperture of 151mm, this astrograph offers significant light-gathering capability, allowing you to capture faint details in distant galaxies and resolve fine structures within emission nebulae. The native f/7 focal ratio strikes a balance between image brightness and image scale, making it well-suited for a wide range of deep-sky targets without requiring excessively long sub-exposures.

Framing Targets with a 1057mm Focal Length

With a focal length of 1057mm, the 151PHQ provides the image scale necessary for resolving details in small to medium-sized deep-sky objects. This reach is ideal for capturing the spiral arms of galaxies like the Whirlpool Galaxy (M51), the intricate structures of planetary nebulae like the Ring Nebula (M57), and the core regions of larger targets like the Orion Nebula (M42).

This focal length produces a tight frame on many popular targets when used with full-frame sensors, emphasizing the object against the sky background. For imagers working with smaller APS-C sensors, the 1057mm focal length offers even greater magnification, making it a powerful tool for isolating smaller galaxies or details within larger nebular complexes.

A Flat 60mm Image Circle: No Flattener Needed

Unlike most refractors that require a separate, external field flattener, the Askar 151PHQ has the flattener integrated into its main optical design. This self-flattening system is designed to produce a corrected, flat image field across a massive 60mm image circle. This eliminates the need to purchase an accessory flattener, calculate its precise back focus, and manage additional connections in your imaging train.

You can connect your camera through the included adapters, focus and shoot. The spot diagram is fine, with tiny distortion of the peripheral stars across the 60mm medium-frame image circle.

Camera Connection: The 4-Piece Adapter System

The 151PHQ is designed for straightforward camera integration. It ships with a set of four threaded adapters to connect your imaging equipment to the focuser's M86 male thread.

• M86×1 to M68×1: The first step-down.
• M68×1 to M54×0.75: The second step-down.
• M54×0.75 to M54×0.75: A simple extension tube.
• M54×0.75 to M48×0.75: The final adapter provides a male M48×0.75 thread and includes a built-in M48×0.75 filter thread for mounting standard 2-inch (M48) filters.

The maximum accessory connection is 78mm from the base of the M48×0.75 male thread with the focuser fully retracted.

Focuser Mechanics: A 3.4-inch Rack-and-Pinion with 360° Rotation

The 151PHQ is equipped with a robust 3.4-inch rack-and-pinion focuser that comes with the M68/M54/M48 adapters, a 360° rotator and a finder base.

For effortless framing of your target, a 360° rotator is integrated into the focuser assembly. This allows you to rotate your imaging train to the desired orientation. Once your composition is set, a locking screw secures the rotator in place. Askar's locking-screw diagram marks screw positions that can be used for electric focusing bracket installation (some screws are factory presets that should not be adjusted).

Optional 0.7x Reducer: An f/4.9 System at 740mm

For imagers seeking a wider field of view and faster imaging times, Askar makes an optional 3-inch 0.7x full-frame reducer for the 107PHQ, 130PHQ and 151PHQ (a triplet with one ED glass). It transforms the astrograph into a 740mm f/4.9 system, significantly shortening required exposure times by nearly half. This speed is a major advantage when capturing faint, expansive nebulae or collecting data for large mosaic projects.

The reducer's back focus is the standard 55mm, and it comes with M68, M54 and M48 thread adapters.

Sensor & Imaging Train Compatibility

The 60mm image circle is larger than a full-frame sensor's diagonal.

• Full-Frame (36x24mm): The 43mm diagonal sits inside the 60mm image circle.
• Medium frame: A medium-frame 60mm image circle.
• Imaging Train: With up to 78mm available from the base of the M48×0.75 thread, you can plan room for an off-axis guider (OAG), a filter wheel or drawer, and any necessary adapters for your specific camera.

Mechanical Design and Stray Light Control

The Askar 151PHQ has a high-quality CNC machined and painted tube with a telescopic lens hood; in observing mode the length grows from 930.3mm with the hood contracted to 1117.8mm with it fully stretched. The hood blocks off-axis light.

The focuser also includes a standard finder base, allowing you to mount your preferred guide scope or finder scope for target acquisition and autoguiding.

A 13.7 kg Platform: Rings, Handle, and 300mm Dovetail

This astrograph is a substantial instrument, with an OTA weight of 11.6 kg and a total weight of 13.7 kg when equipped with the included mounting hardware. This requires a high-capacity equatorial mount to ensure stable, precise tracking for long-exposure astrophotography. The package includes a complete set of hardware for immediate mounting.

A sturdy double tube ring holds the optical tube, and a multi-function carrying handle is bolted to the top. This handle simplifies transport and setup and includes a slot for M6 screws to attach accessories. For mounting, a 300mm Losmandy-style dovetail plate is provided, offering a long, rigid connection to your mount saddle.

Askar 151PHQ vs. 130PHQ: Light Grasp and Image Scale

Askar launched the 151PHQ after the 130PHQ as the biggest refractor of the PHQ series.

• Askar 151PHQ Advantage: With a 151mm objective, the 151PHQ gathers approximately 34% more light than the 130mm model. This allows you to capture fainter details or reduce exposure times for the same signal-to-noise ratio.