Wanderer Astro 4+1 FilterCube 2"/50mm for RASA 11/36

The FilterCube 50: Zero-Obstruction Imaging for RASA 11/36

The FilterCube 50 (WFC50) solves the primary challenge of prime-focus imaging: adding filtration without obstructing the optical path. Designed for the Celestron RASA 11 and RASA 36, it is described by Wanderer Astro as the first zero-optical-obstruction 5-slot motorized filter wheel compatible with RASA 11/36 systems. This allows you to perform LRGB and narrowband imaging sequences without adding optical obstruction to these fast optical systems.

By integrating a camera angle adjuster and a tilt plate directly into its housing, the FilterCube also consolidates multiple accessories into a single, rigid unit. This simplifies your imaging train and provides camera angle and tilt adjustment, with the filter wheel itself controlled via a single USB-C cable and an ASCOM driver.

A 114 mm Diameter for Unobstructed Prime-Focus Imaging

The key to the FilterCube's design is its 114 mm outer diameter. At this size the FilterCube introduces zero optical obstruction when installed on a RASA 11 or RASA 36, so it adds multi-filter capability without adding to the obstruction in the light path.

The FilterCube is not compatible with RASA 8 or HyperStar systems, because of the FilterCube's minimum back focus of 60.3 mm. For RASA 11 and 36 imagers, however, the WFC50 offers a complete and unobtrusive filtration solution.

Patented 4+1 Side-Flip Filter System

Instead of a traditional carousel, the FilterCube uses a patented mechanism with four side-mounted filter trays that flip into the optical path. A fifth filter, typically a Luminance (L) filter, is installed in a fixed position in the center of the wheel.

In this "4+1" configuration the central L-filter can be used on its own or in combination with any of the four side-flip filters (e.g., R, G, B, Ha): a side filter flipped into the path is stacked on top of the central filter. The selection of all five positions is motorized and controlled via software.

Support for 2" Mounted and 50 mm Unmounted Filters

The FilterCube offers the flexibility to use a mix of common filter formats. It accepts standard 2" mounted filters and 50 mm round unmounted filters, which can be installed together in the same unit. This allows you to use filters you may already own without needing to purchase a new, dedicated set.

• 2" Mounted Filters: Supports filters with a standard M48x0.75 thread. The cell height (excluding threads) must be 6 mm or less, and the thread length must be 3 mm or less to ensure clearance.
• 50 mm Unmounted Filters: Accommodates unmounted glass with a thickness between 1.9 mm and 3.5 mm. Filters thinner than 2.5 mm require filter shims (sold separately).
• Thick Filter Cells: If you own 2" filters with cells taller than 6 mm, which may get stuck, Wanderer Astro offers an optional Low Profile Filter Cell Replacement Kit to ensure compatibility.

60.3 mm Optical Thickness and Camera Compatibility

The FilterCube adds a total of 60.3 mm of optical thickness to the light path. This back focus consumption dictates which cameras are compatible with the RASA 11 and RASA 36 systems.

• RASA 11 Compatibility: On a RASA 11, the FilterCube works directly with cameras that have a native back focus of 12.5 mm or less.
• RASA 36 Compatibility: For use with a RASA 36, you will need the RASA36 adapter kit (sold separately). With this adapter, the FilterCube supports cameras with a back focus of up to 17.5 mm, such as the Moravian C1x series.

The rear tilt adjuster has screw through-holes for ZWO, QHYCCD, Player One and ToupTek APS-C and full-frame cameras, so the camera bolts directly to it.

Integrated CAA, 3-Point Tilt Adjuster, and Collimation Access

The FilterCube is engineered for precise optical alignment. A manual Camera Angle Adjuster (CAA) is built into the body, allowing you to rotate your camera for framing. The rear of the unit incorporates a 3-point tilt adjuster plate, enabling you to correct sensor tilt.

Collimating the RASA with the FilterCube installed is also straightforward. The housing features access slots designed for a hex wrench to pass through to the RASA's collimation screws. If a slot is blocked, you can either slightly rotate the entire FilterCube or remove the rear barrel and reinstall it at a 90-degree offset to gain clear access.

A 385 g Anti-Reflection Design for Maximum Rigidity

Constructed from aluminum alloy with partial carbon fiber components, the FilterCube weighs only 385 g. Internally, the device has undergone extensive testing to optimize its mechanical dimensions and apply anti-reflection measures, to minimize common RASA imaging issues such as ghosting, rainbow artifacts, strange halos and flat frame calibration problems.

For added security, the removable rear housing is secured by two set screws and two safety clips. Working alongside the set screws, the clips help eliminate the risk of equipment detachment from improperly tightened set screws.

Step-by-Step Filter Installation and Calibration

Installing filters is a precise process guided by the software. First, loosen the two set screws and remove the rear barrel. After connecting the FilterCube to a PC via the USB-C cable, use your imaging software (like N.I.N.A.) to select the specific filter slot you wish to populate. It is critical to install the central L-filter first, as space becomes limited once the side filters are in place. Use the provided M2x4 screws to secure the filter masks, as these also serve a positioning function.

Once all filters are installed, re-attach the rear barrel and tighten the set screws. As a final step, cycle through all five filter positions in the software (e.g., 1-2-3-4-5-1). This calibrates the filter positioning before real imaging.

Connecting Cameras and the RASA Optical Tube

To attach your camera, first remove the FilterCube's rear tilt adjuster. Attach the adjuster plate to the camera from the back using the appropriate screws (M2.5x10, M2.5x6, or M3x5 sets are included), then reinstall the camera and adjuster assembly onto the FilterCube. If your camera has an outer diameter smaller than 85 mm, use the included black sealing stickers to cover the unused outer screw holes and prevent light leaks.

To mount the entire assembly to the telescope, slide the RASA's original factory retaining ring onto the rear barrel of the FilterCube. Then, simply screw the retaining ring onto the RASA. As instructed in Celestron's RASA white paper, you must remove the RASA's clear optical window before installing the FilterCube.

WandererEmpire Software: ASCOM Control for up to 4 FilterCubes

The FilterCube is controlled via the WandererEmpire software suite, which includes the ASCOM driver for use in ASCOM imaging software such as N.I.N.A. A single USB 2.0 Type-C cable provides both 0.5 A of power and data control, eliminating the need for a separate 12V power supply.

In your imaging software, you can connect to the FilterCube, assign names to each filter position (e.g., "Luminance," "Ha 7nm"), and set per-filter focus offsets. For advanced setups, the driver supports independent control of up to four FilterCubes from a single computer. This is ideal for multi-telescope arrays or sky survey projects where multiple RASAs are operated in parallel.

Managing Focus Shift with the Central L-Filter

When you use the central L-filter in combination with one of the four side-flip filters, the total glass thickness in the optical path increases. While this does not negatively affect image quality on a RASA, it does cause a significant focus shift. This shift is large enough to cause autofocus and plate-solving routines to fail if not accounted for.

The solution is to plan your sequences accordingly. In software like N.I.N.A., you can record the approximate focus position for the L-filter alone and for the combined L+narrowband filters. When switching between them in an advanced sequence, insert a command to move the focuser to the approximate focus position before running autofocus or plate solving. This ensures stars are detectable and the automated routines can succeed.