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William Optics
William Optics RedCat 51
A compact Petzval refractor delivering exceptionally sharp wide-field photography and visual performance.
From the community
What owners say
Based on 24 Cloudy Nights discussions
What they love
- ✓Exceptional optical sharpness compared to high-end camera lenses (Nikon 200mm f/2, 300mm lenses)
- ✓Excellent fit and finish quality throughout the telescope
- ✓Superb packaging and case design
- ✓Easy to use overall
- ✓Sharp focus across all four corners of the field
What caught them off guard
- !Focuser is initially stiff and may require break-in period
- !Canon EOS adapter has significant play (approximately 15 degrees of movement)
- !Vixen dovetail is undersized and does not fit properly in some Arca Swiss mounts
- !Case is too small to fit the scope with diagonal and dew shield attached in visual configuration
- !Documentation lacks specification of Allen wrench sizes needed for assembly
Top targets reported by owners
What you'll see
Moon
described as sharp and detailed in cropped Canon 60D images
Terrestrial wildlife at distance
Great Blue Herons at 150-600 feet, Bald Eagles at 1800 feet, Cardinals, Gambel Quail captured with m…
Bright field stars for astrophotography
users report sharp star shapes across field when properly focused and with correct back-spacing
Wide field deep-sky imaging
marketed for this purpose with flat field across full frame sensors
Worth knowing before you buy
Canon EOS adapter has approximately 15 degrees of movement/play once mounted, does not click tight securely
Vixen dovetail on the scope is too small and does not grip properly in standard Vixen saddles, requiring improvised solu…
Some early units exhibited coma-like aberrations in star shapes, particularly at the edges of the field, with opposite o…
Frequently asked
Questions from owners
Sourced from Cloudy Nights discussions.
- Will my camera adapter work without vignetting?
- You must use the correct camera-specific adapter from William Optics—using incorrect adapters (like T-mount to Canon adapters chained together) causes significant vignetting. The Sony E-mount adapter is described as very well-made and fits snugly; the Canon EOS adapter has about 15 degrees of movement and does not click tight, which may cause alignment issues.
- Does it have a flat field suitable for astrophotography?
- Users report mixed results. While some see sharp stars across the full frame with the correct backspacing, others have detected coma in the corners and occasional tilt issues in early units.
- What is the back focus situation for visual observing?
- The scope does not have enough back focus for standard eyepieces in typical diagonals—a significant quirk for a visual instrument. Owners must use the proprietary WO Amici diagonal or adapt non-standard solutions; the rear port is M56×0.
- Is the manual focus ring difficult to use?
- Multiple owners describe the focus ring as stiff but usable without backlash. The included Bahtinov mask design is effective for precise focusing.
- Will the Vixen dovetail mount securely on my tripod?
- The Vixen dovetail is undersized and may not grip securely in standard Vixen saddles designed for full-size telescopes. Users report the dovetail is too small for some mounts and have had to use workarounds like wedging twigs or adapting ADM bars.
- What accessories or tools should I buy with it?
- The scope requires multiple Allen wrenches of unspecified sizes (WO does not include a tool list or hex keys with all units). The correct camera adapter for your specific mount is essential and must be ordered separately from WO.
Full Specifications
Optics
| Aperture | 51mm |
| Focal Length | 250mm |
| Focal Ratio | f/4.9 |
| Optical Design | Refractor |
| Lens Elements | 4-element |
| Coatings | Fully multi-coated Petzval design on all surfaces |
Mount & Tracking
| GoTo (Computerised) | No |
| Tracking | No |
Focuser
| Focuser Size | 2" / 1.25" |
| Focuser Type | Dual-speed Crayford with micro-focuser |
Physical
| OTA Weight | 1.35kg |
| Tube Length | 232mm |
| Tube Material | Aluminium, anodised red |
Included Accessories
| Diagonal | No |