William Optics
William Optics Cat 91 WIFD · 30th Anniversary Limited Edition
William Optics Cat 91 WIFD · 30th Anniversary Limited Edition
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The Cat 91 WIFD · 30th Anniversary Edition is a commemorative refractor celebrating three decades of William Optics craftsmanship and innovation. Built upon the acclaimed five-element advanced Petzval optical design, this limited edition of 30 units worldwide combines uncompromising astrophotography performance with a symbolic anniversary finish.
Featuring a unique laser-engraved emblem of a cat embracing “30” and accompanied by a 30th Anniversary Certificate, the Cat 91 WIFD is not only a professional imaging instrument but also a collector’s piece that honors the Cat series legacy.
Highlights:
Petzval Design, No Backfocus Hassles
The 5-element Petzval design eliminates the need for backfocus adjustments, providing sharp, edge-to-edge images with pinpoint stars—ideal for wide-field and detailed astrophotography alike.
Full-Frame & Medium-Format Ready, No Extra Flattener Needed
With a large 55mm image circle, the Cat 91 is perfect for both full-frame and medium-format cameras. Its advanced optics achieve flat-field images without requiring an additional flattener, giving astrophotographers the freedom to capture expansive views with unparalleled clarity.
Fast f/4.9 Focal Ratio
The Cat 91's fast f/4.9 focal ratio is designed for bright, vivid captures of galaxies, nebulae, and beyond, ensuring excellent light-gathering power and sharp detail even on faint celestial objects.
Seamless WIFD Focusing
Equipped with William Optics' WIFD focuser, the Cat 91 provides precise, stable focusing without additional adjustments, enhancing the ease of use for both seasoned astrophotographers and beginners.
- Lens Type
- 5-Element Advanced Petzval
- Lens Elements
- Super ED Glass x2 ED Glass x1 Lanthanum Glass x1 X-Element x1
- Focal Length
- 448 mm
- Diameter
- 91 mm
- Focal Ratio
- f/4.9
- Image Circle
- 55 mm
- Focuser
- WIFD R&P Focuser Compatible with EAF
- Focuser Travel
- 0-36 mm (Ruler to 40mm)
- Back Spacing
- Maximum: M48 (60.8mm),M54 (65.8mm)
- Adapter Included
- Tilt Adjuster Rotator M63 → M54 Adapter M63 → M48 Adapter
- Optional Flattener
- No Flattener Required
- T-Mount Support
- Canon EF, RF Nikon F, Z Sony E Pentax K MFT (M4/3) FUJI X
- Camera Format
- Medium Format (needs additional adapter) Medium Format APS-C M4/3
- Dovetail Type
- Vixen
- Tube Length
- 556 mm
- OTA Weight
- 4.72 kg / 10.41 lbs
- Total Weight
- 6.3 kg / 13.89 lbs
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