William Optics MiniCat 51 WIFD f/3.5

6-Element f/3.5 Petzval Optics: A 43.2mm Flat Field

The MiniCat 51's optical system is built for one purpose: capturing immense swaths of the night sky with exceptional color correction and sharpness. The 6-element Petzval layout corrects for field curvature internally, meaning you get pinpoint stars across a 43.2mm image circle without the complexity of a separate flattener. Two Super ED elements minimize chromatic aberration, ensuring clean, high-contrast images of targets like the North American Nebula (NGC 7000) or the Andromeda Galaxy (M31).

At an aggressive f/3.5 focal ratio, this astrograph gathers light significantly faster than typical f/5 or f/6 refractors. This allows you to collect more signal in less time, reducing the demands on your mount's tracking and enabling deeper images from a single night's session.

Patented WIFD Focuser: 28mm of Tilt-Free Travel

William Optics' patented Internal Focus Design (WIFD) is a robust rack-and-pinion mechanism built to handle modern imaging payloads without flexure or tilt. The entire focusing mechanism moves internally, providing 28mm of precise travel while maintaining perfect optical alignment. This design is critical for maintaining a flat field, as it prevents the drawtube sag that can compromise edge-of-field star shapes.

• EAF Compatible: The focuser is designed for seamless integration with the ZWO EAF and other popular electronic focusers for automated, repeatable focusing.
• Flexible Back Spacing: With a working distance of 58mm to 30mm, you have ample room to incorporate filter wheels, off-axis guiders, and other accessories into your imaging train.
• Included Rotator & Tilt Adapter: The package includes a camera angle rotator and tilt adjuster, giving you full control over framing and sensor plane alignment right out of the box.

Vixen & Arca-Swiss Mounting: 1.67 kg for Any Mount

Engineered for portability, the MiniCat 51 OTA weighs a mere 1.67 kg and has a compact 210mm tube length. This makes it an ideal match for lightweight star trackers and portable GoTo mounts, allowing you to build a powerful imaging rig that travels easily. The integrated dual-spec dovetail plate provides native compatibility with both traditional Vixen-style saddles and modern Arca-Swiss tripod heads, offering maximum flexibility for mounting.

MiniCat 51 vs. RedCat 51: Focal Ratio and Focuser Design

While both astrographs share a 51mm aperture, the MiniCat 51 is a distinct instrument from its sibling, the RedCat 51. The choice between them depends on your specific imaging goals.

• RedCat 51 Advantage: The RedCat 51's 250mm focal length (f/4.9) provides slightly more image scale for smaller deep-sky objects. Its helical focuser is simple and robust for manual focusing.
• MiniCat 51 Advantage: The MiniCat 51 is significantly faster at f/3.5 and offers a wider 178mm focal length, making it superior for capturing enormous nebulae and multi-panel mosaics. Its WIFD rack-and-pinion focuser is built from the ground up for EAF automation and heavier camera loads, eliminating the image shift that can occur with helical focusers during autofocus routines.