William Optics RedCat 91 WIFD
William Optics
William Optics RedCat 91 WIFD is a 91 mm Petzval APO refractor for wide-to-mid-field nebulae and general deep-sky imaging.
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Specifications
Optics
- Optical design
- Petzval APO refractor
- Aperture
- 91 mm
- Focal length
- 448 mm
- Focal ratio
- f/4.9
- Dawes limit
- 1.27"
- Glass / elements
- Petzval APO objective
Imaging
- Image circle
- 55 mm
- Camera format
- Full frame / APS-C / Micro 4/3
- Full-frame coverage
- Yes
- Back focus
- No flattener required
- Corrected field
- Native flat imaging field
Specifications
- Weight
- 10.41 lb (4.72 kg)
Mechanical
- Focuser
- WIFD rack-and-pinion internal focuser
Astrophotography Fit
Best for wide-to-mid-field nebulae and general deep-sky imaging when the mount, camera format, and correction hardware are chosen as one system.
William Optics RedCat 91 WIFD sits in the telescope slot for wide-to-mid-field nebulae and general deep-sky imaging. The useful headline specs are aperture 91 mm, focal length 448 mm, f/4.9.
Camera coverage: Full frame / APS-C / Micro 4/3. Image circle: 55 mm. Back focus: No flattener required.
Fast astrographs collect signal quickly, but they are unforgiving: collimation, tilt, filter behavior, and back-focus spacing show up immediately in star shapes.
Best paired with
- Rigid focuser, tilt adjuster, and exact corrector spacing
- Cooled cameras with a sensor inside the corrected image circle
- High-throughput filters that behave well at fast focal ratios
Not recommended for
- Users who do not want to tune collimation, tilt, and spacing
- Thick or narrow filters that show strong bandpass shift at fast focal ratios
- Loose camera adapters or focusers that cannot hold the imaging train square
Where To Buy
Some links on this page are affiliate links. Prices and availability are pulled automatically from each retailer and updated daily.
| Retailer | Price | Availability | View Offer |
|---|---|---|---|
| Cloud Break Optics Cloud Break Optics | $2,998.00 | In stock Updated 5/11/2026 | View Offer - $2,998.00 |
| High Point Scientific High Point Scientific | $2,998.00 | In stock Updated 5/12/2026 | View Offer - $2,998.00 |
| Mile High Astronomy Mile High Astronomy | $2,998.00 | In stock Updated 5/12/2026 | View Offer - $2,998.00 |