ZWO FF131 APO Refractor w/ AM5N Astrophotography Bundle

The ZWO FF131 & AM5N Bundle: A Complete 131mm Imaging Platform

This bundle is a complete astrophotography system engineered by ZWO for imagers who require large aperture and a portable, high-precision mount. It includes four core components: the FF131-APO quadruplet refractor, the AM5N harmonic drive mount, the TC40 carbon fiber tripod, and the PE200 pier extension. Together, they form a turnkey solution for capturing deep-sky objects with full-frame cameras.

The system is designed for the serious astrophotographer who wants to minimize setup complexity without sacrificing optical quality or tracking stability. The self-flattening 131mm refractor eliminates the need for external correctors, while the counterweight-free design of the AM5N mount reduces total system weight and setup time. This suits both backyard observatories and trips to remote dark-sky sites.

Payload Matching: The 20.72 lb. FF131 on the 33 lb. Capacity AM5N

The engineering synergy of this bundle begins with the payload match between the telescope and mount. The FF131-APO optical tube, fully equipped with its handle, mounting rings, and 300mm Losmandy-style dovetail, has a total weight of 20.72 lb. This is well within the 33 lb. counterweight-free capacity of the AM5N mount.

This leaves a substantial payload margin of over 12 lb. for your imaging equipment. You can confidently add a large sensor camera, a filter wheel, an off-axis guider, and a guide camera without approaching the mount's operational limits. This generous headroom ensures the harmonic drive operates smoothly, delivering its stated tracking accuracy of <±10 arcseconds for sharp, untrailed long exposures.

FF131 Quadruplet Optics: A 131mm f/7.5 Apochromatic Design

The heart of this imaging system is the FF131's 4-element quadruplet optical design. With a 131mm (5.15") aperture and a 983mm focal length, the telescope operates at a native f/7.5. This apochromatic ("APO") design uses four air-spaced lenses, including one ED (Extra-low Dispersion) glass element, to bring different wavelengths of light to a single, sharp focal point. This minimizes chromatic aberration, or color fringing, for high-contrast images with accurate color rendition.

The 131mm aperture provides significant light-gathering power, allowing you to resolve fine details in distant galaxies and capture faint nebulosity. The 983mm focal length delivers an image scale well-suited for a wide range of deep-sky targets, from medium-sized nebulae like the Dumbbell Nebula (M27) to smaller galaxies, especially when paired with modern high-resolution CMOS sensors.

The FF131's 44mm Image Circle: Native Flat-Field Full-Frame Coverage

A key feature of the FF131-APO is its self-flattening optical design, which produces a 44mm corrected image circle. This is large enough to cover the 43.3mm diagonal of a full-frame sensor, ensuring sharp, point-like stars across the entire field of view without vignetting. This integrated correction simplifies your imaging train by making a separate field flattener unnecessary.

This design eliminates the tedious process of calculating and setting a precise back focus distance. Your camera's sensor simply needs to be placed within a generous focus range of 42mm to 73mm from the M48x0.75 thread on the included photography extension tube. This flexibility easily accommodates most filter wheels, off-axis guiders, and camera combinations.

FF131 Mechanics: A 3" Dual-Speed Focuser with 360° Rotation

The FF131-APO is equipped with a heavy-duty 3" rack and pinion focuser designed to carry heavy imaging loads without flexure or slippage. It provides 31mm of focuser travel and features a dual-speed mechanism with a 1:10 ratio fine-adjustment knob, allowing for the precise, critical focus adjustments needed for high-resolution astrophotography.

To aid in framing your target, the focuser includes a built-in 360° rotator, letting you set your camera's orientation without loosening any connections. The focuser body is also pre-drilled for an EAF (Electronic Automatic Focuser) bracket, allowing for easy integration with ZWO's automated focusing system (sold separately). The retractable dew shield, with a 157mm outer diameter, protects the objective from moisture and stray light while reducing the telescope's transport length to 878mm.

The AM5N Mount: A 12.1 lb. Head with Harmonic Drive and <±10" PE

The AM5N mount head weighs just 12.1 lb. yet delivers the performance of a much heavier mount. Its strain-wave gear and synchronous belt system provide a high 300:1 reduction ratio, enabling precise tracking with a native periodic error of less than ±10 arcseconds over a 288-second cycle. This level of accuracy, even before autoguiding, is fundamental to capturing sharp, long-exposure images.

The harmonic drive delivers high torque, which is what allows the mount to handle its 33 lb. payload without counterweights. When moving between targets, the mount can slew at up to 6° per second, minimizing downtime in your imaging sequence. Each mount is factory-tested for periodic error, and a unique performance sheet is included in the box.

AM5N Control: Equatorial/Alt-Az Modes, Wi-Fi, and ASCOM

The AM5N is a versatile mount that can operate in both Equatorial mode for astrophotography and Alt-Azimuth mode for visual observing. You can control the mount through multiple interfaces, including the included hand controller, a smartphone or tablet via integrated Wi-Fi and Bluetooth, or a PC through its USB port. This flexibility suits any workflow, from a fully wireless field setup to a computer-controlled observatory.

For advanced imaging, the mount supports both ASCOM and INDI drivers, ensuring compatibility with popular automation software like NINA and SGP. It also integrates into the ZWO ecosystem via the ASIAIR app. A standard ST4 port is also provided for direct connection to an autoguiding camera.

Support System: The 5.07 lb. TC40 Tripod and 200mm PE200 Pier

This bundle includes a complete support system matched to the mount and telescope. The TC40 tripod uses 1.5" diameter carbon fiber legs to provide a rigid, vibration-dampening foundation that weighs only 5.07 lb. yet supports up to 110.23 lb. Its height adjusts from 18.5" to 31.49", allowing you to achieve a low center of gravity for maximum stability.

To prevent the 878mm-long FF131 from colliding with the tripod legs when pointing near the zenith, the bundle also includes the PE200 pier extension. This aircraft-grade aluminum extension adds exactly 200mm of height between the tripod and the mount head, ensuring safe clearance for your telescope and camera during automated meridian flips.

Mount Power System: 12V 3A Operation with Power-Off Protection

The AM5N mount requires a stable 12V DC power source capable of delivering at least 3A of current to handle high-torque slews. The mount features an under-voltage protection circuit that will sound an audible alarm if the input voltage drops below 10.8V, alerting you to a potential power issue before it affects tracking.

A critical safety feature is the mount's power-off brake protection. In the event of an unexpected power loss, a mechanical brake on the Right Ascension axis engages automatically. This prevents the telescope from swinging freely, protecting your optical tube and expensive camera from impact damage.

Imaging with the FF131 & AM5N Bundle: From Setup to Final Frame

This bundle is purpose-built for an efficient imaging workflow. After assembling the system, you attach your camera and any accessories like a filter wheel or off-axis guider. With the native flat-field optics, you only need to achieve sharp focus using the 3" dual-speed focuser; no complex corrector spacing is required. Adding a guide scope to one of the two included findershoes and connecting a guide camera to the ST4 port enables high-precision autoguiding.

For visual observation, the 3" focuser accepts a standard 2" star diagonal. With the AM5N set to Alt-Azimuth mode, you can use a low-power 2" eyepiece for wide-field views of star clusters or switch to a high-power 1.25" eyepiece for detailed views of the Moon and planets. The apochromatic optics provide crisp, high-contrast images free of distracting color fringing.

First Night Setup: A 5-Step Guide to Assembling Your Rig

Getting this bundle ready for imaging is a streamlined process. The counterweight-free design and matched components simplify assembly, letting you get on sky faster.

• Step 1: Assemble the Support. Set up the TC40 tripod and attach the 200mm PE200 pier extension. Level the tripod using its adjustable legs.
• Step 2: Mount the AM5N. Secure the 12.1 lb. AM5N mount head to the top of the pier extension. Adjust the latitude setting to match your location.
• Step 3: Attach the Telescope. Mount the FF131-APO's 300mm Losmandy-style dovetail into the AM5N's dual saddle. At 20.72 lb., the telescope does not require balancing.
• Step 4: Perform Polar Alignment. Connect power to the mount. Use your imaging camera and a software routine, like the one in the ASIAIR app, to perform a precise polar alignment by adjusting the mount's altitude and azimuth controls.
• Step 5: Focus and Frame. Attach your camera, point to a bright star, and use the 3" dual-speed focuser to achieve critical focus. Use the 360° rotator to frame your target, and you are ready to begin your imaging session.