William Optics RedCat 91 WIFD f/4.9 Petzval Refractor Telescope - Space Gray
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Special Limited Edition - Limited to stock on hand only
- An internal focusing design moves the lens elements inside the tube rather than racking a heavy drawtube out the back, eliminating camera tilt, flexure, and vignettes while remaining fully compatible with electronic focusers like the ZWO EAF
- A premium 5-element Petzval design natively corrects and illuminates up to Medium Format sensors with tack-sharp stars from corner to corner—no external field flattener required
- Stepping up to a larger 91mm aperture and a versatile 448mm focal length (f/4.9), it delivers far more light-gathering muscle and deep-sky reach than smaller RedCat models
William Optics RedCat 91 WIFD: A Beast in the RedCat Lineup
Introducing the William Optics RedCat 91 WIFD sleek Space Grey refractor. Built around a groundbreaking 5-element advanced Petzval optical design, the RedCat 91 expands on the iconic portable refractor series that astrophotographers of all skill levels have raved about for years. This limited-edition powerhouse brings a significantly larger 91mm aperture and a deeper 448mm focal length to the table, providing the extra light-gathering muscle and reach you need for faint deep-sky targets while maintaining the signature, pinpoint, flat-field star quality the series is famous for.
More than just a focal length upgrade, the RedCat 91 is an engineering masterpiece. It features William Optics' patented WIFD (William's Internal Focusing Design) system, meaning the focuser draws internally to completely eliminate heavy camera tilt and vignette issues while maintaining electronic focus compatibility (like the ZWO EAF) straight out of the box. This refractor comes with essentail tools like a multi-functional handle, built-in Bahtinov mask lens cap and a camera angle rotator; all while effortlessly illuminating up to a 55mm image circle (Medium Format). It’s not just a giant leap forward in wide-field imaging performance—it’s a stunning piece built for the next generation of astrophotography.
Full Frame Image Circle & Pinpoint Corner Stars
The RedCat 91 features 5 total lens elements, arranged in what William Optics calls an "advanced Petzval design" (consisting of 2 "super" ED (SD), 1 ED, 1 lanthanum and 1 undisclosed element lenses). This results in a huge 55mm image circle, which is not just full frame compatible, but nearing medium format sensor territory. We strongly recommend checking out the spot diagram below — note how small the spot sizes are even at a radius of 21.6mm (bottom right chart), which is where the stars would be in the corners of a full frame sensor
WIFD Focuser: EAF Compatible
The RedCat 91 features the same high-quality focuser in the rest of the RedCat line, William Optics' patented William Optics Internal Focus Design (WIFD) focuser. This innovative focuser design moves the focus drawtube and lens elements all internally. This has a number of large benefits for astrophotographers.
First and foremost, it can support heavy image trains with large filter wheels, cameras, and rotators without introducing any tilt, though a tilt adapter is still included just in case. Second, any vignetting caused by the focuser is eliminated due to the design. Third, because the drawtube is entirely internal, the telescope's overall length does not change when changing focus. Simply put, the WIFD is one of the best focuser designs available in consumer telescopes. It is also compatible with third-party electronic focusers like the ZWO EAF out of the box.
Portability & Soft Travel Case Included
Weighing just 14 lbs (6.3 kg) total with the included tube rings and dovetail plate, the RedCat 91 remains incredibly portable and is small enough to fit in a standard overhead carry-on bag. A soft carry case is included, keeping your RedCat 91 safe & protected during any type of travel.
RedCat 91 Focal Length, Aperture, and Focal Ratio
The RedCat 91's focal length is 448mm, which makes it perfect for photographing medium focal length reach targets like large galaxies and nebulae. The aperture as the name implies is 91mm, which is a significant step up over the RedCat 51, 61, and 71. This larger aperture allows for capturing higher resolution on detailed objects. Lastly, the RedCat 91's focal ratio is f/4.9, which is the same fast focal ratio found on the rest of the RedCat line.
Specifications
-
Lens Type: 5-element Petzval design
-
Aperture: 91 mm (3.58 in)
-
Focal Length: 448 mm
-
Focal Ratio: f/4.9
-
Glass Elements: 2 x Super ED, 1 x ED, 1 x Lanthanum, 1 x Undisclosed Element
-
Image Circle: 50 mm (Full-Frame and Medium Format coverage)
-
Camera Format Support: Medium Format (requires optional adapter), Full Frame, APS-C, Micro Four Thirds (M4/3)
-
T-Mount Compatibility: Canon EF/RF, Nikon F/Z, Sony E, Pentax K, Micro Four Thirds (M4/3), FUJI X
-
Focuser Type: WIFD Rack & P inion focuser (ZWO EAF electronic focuser compatible)
-
Focuser Travel: 36 mm (features 0–40 mm physical mark ings)
-
Focuser Features: Focus lock knob and integrated thermometer scale
-
Maximum Backfocus (with M48 Adapter): 60.8 mm (2.39 in)
-
Maximum Backfocus (with M54 Adapter): 65.8 mm (2.59 in)
-
Rear-End Mechanical Adapters: integrated camera tilt adjuster, field rotator, M63-to-M54 adapter, and M63-to-M48 adapter
-
OTA Weight (Tube Only): 4.72 kg (10.41 lb)
-
Total instrument Weight: 6.30 kg (13.89 lb) ( includes dual mount ing r ings and large dovetail plate)
-
Total Optical Tube Length: 556 mm (21.89 in)
-
Ma in Tube Outer Diameter: 116.5 mm (4.59 in)
-
Dew Shield Outer Diameter (OD): 120 mm (4.72 in)
-
Dew Shield inner Diameter (ID): 117 mm (4.61 in)
-
Dew Shield Length: 180 mm (7.09 in)
-
Rigging & Mounting: 290 mm (11.42 in) Vixen-style bottom dovetail plate; top multi-functional saddle handlebar
-
Finderscope Mount: Bracket and saddle bar included
- Color: Space Grey finish
Other Information
- Country of Manufacture: Taiwan
William Optics RedCat 91 WIFD: A Beast in the RedCat Lineup
Introducing the William Optics RedCat 91 WIFD sleek Space Grey refractor. Built around a groundbreaking 5-element advanced Petzval optical design, the RedCat 91 expands on the iconic portable refractor series that astrophotographers of all skill levels have raved about for years. This limited-edition powerhouse brings a significantly larger 91mm aperture and a deeper 448mm focal length to the table, providing the extra light-gathering muscle and reach you need for faint deep-sky targets while maintaining the signature, pinpoint, flat-field star quality the series is famous for.
More than just a focal length upgrade, the RedCat 91 is an engineering masterpiece. It features William Optics' patented WIFD (William's Internal Focusing Design) system, meaning the focuser draws internally to completely eliminate heavy camera tilt and vignette issues while maintaining electronic focus compatibility (like the ZWO EAF) straight out of the box. This refractor comes with essentail tools like a multi-functional handle, built-in Bahtinov mask lens cap and a camera angle rotator; all while effortlessly illuminating up to a 55mm image circle (Medium Format). It’s not just a giant leap forward in wide-field imaging performance—it’s a stunning piece built for the next generation of astrophotography.
Full Frame Image Circle & Pinpoint Corner Stars
The RedCat 91 features 5 total lens elements, arranged in what William Optics calls an "advanced Petzval design" (consisting of 2 "super" ED (SD), 1 ED, 1 lanthanum and 1 undisclosed element lenses). This results in a huge 55mm image circle, which is not just full frame compatible, but nearing medium format sensor territory. We strongly recommend checking out the spot diagram below — note how small the spot sizes are even at a radius of 21.6mm (bottom right chart), which is where the stars would be in the corners of a full frame sensor
WIFD Focuser: EAF Compatible
The RedCat 91 features the same high-quality focuser in the rest of the RedCat line, William Optics' patented William Optics Internal Focus Design (WIFD) focuser. This innovative focuser design moves the focus drawtube and lens elements all internally. This has a number of large benefits for astrophotographers.
First and foremost, it can support heavy image trains with large filter wheels, cameras, and rotators without introducing any tilt, though a tilt adapter is still included just in case. Second, any vignetting caused by the focuser is eliminated due to the design. Third, because the drawtube is entirely internal, the telescope's overall length does not change when changing focus. Simply put, the WIFD is one of the best focuser designs available in consumer telescopes. It is also compatible with third-party electronic focusers like the ZWO EAF out of the box.
Portability & Soft Travel Case Included
Weighing just 14 lbs (6.3 kg) total with the included tube rings and dovetail plate, the RedCat 91 remains incredibly portable and is small enough to fit in a standard overhead carry-on bag. A soft carry case is included, keeping your RedCat 91 safe & protected during any type of travel.
RedCat 91 Focal Length, Aperture, and Focal Ratio
The RedCat 91's focal length is 448mm, which makes it perfect for photographing medium focal length reach targets like large galaxies and nebulae. The aperture as the name implies is 91mm, which is a significant step up over the RedCat 51, 61, and 71. This larger aperture allows for capturing higher resolution on detailed objects. Lastly, the RedCat 91's focal ratio is f/4.9, which is the same fast focal ratio found on the rest of the RedCat line.
Specifications
-
Lens Type: 5-element Petzval design
-
Aperture: 91 mm (3.58 in)
-
Focal Length: 448 mm
-
Focal Ratio: f/4.9
-
Glass Elements: 2 x Super ED, 1 x ED, 1 x Lanthanum, 1 x Undisclosed Element
-
Image Circle: 50 mm (Full-Frame and Medium Format coverage)
-
Camera Format Support: Medium Format (requires optional adapter), Full Frame, APS-C, Micro Four Thirds (M4/3)
-
T-Mount Compatibility: Canon EF/RF, Nikon F/Z, Sony E, Pentax K, Micro Four Thirds (M4/3), FUJI X
-
Focuser Type: WIFD Rack & P inion focuser (ZWO EAF electronic focuser compatible)
-
Focuser Travel: 36 mm (features 0–40 mm physical mark ings)
-
Focuser Features: Focus lock knob and integrated thermometer scale
-
Maximum Backfocus (with M48 Adapter): 60.8 mm (2.39 in)
-
Maximum Backfocus (with M54 Adapter): 65.8 mm (2.59 in)
-
Rear-End Mechanical Adapters: integrated camera tilt adjuster, field rotator, M63-to-M54 adapter, and M63-to-M48 adapter
-
OTA Weight (Tube Only): 4.72 kg (10.41 lb)
-
Total instrument Weight: 6.30 kg (13.89 lb) ( includes dual mount ing r ings and large dovetail plate)
-
Total Optical Tube Length: 556 mm (21.89 in)
-
Ma in Tube Outer Diameter: 116.5 mm (4.59 in)
-
Dew Shield Outer Diameter (OD): 120 mm (4.72 in)
-
Dew Shield inner Diameter (ID): 117 mm (4.61 in)
-
Dew Shield Length: 180 mm (7.09 in)
-
Rigging & Mounting: 290 mm (11.42 in) Vixen-style bottom dovetail plate; top multi-functional saddle handlebar
-
Finderscope Mount: Bracket and saddle bar included
- Color: Space Grey finish
| Manufacturer | William Optics |
|---|---|
| Telescope Focal Length | 401 - 500mm |
- 1x RedCat 91 - Space Gray
- 1x Dust cover w/ bahtinov mask
- 1x Saddle handlebar
- 1x Tube rings
- 1x Camera angle rotator
- 1x Tilt adapter
- 1x 290mm Vixen-style dovetail plate
- 1x M63 to M48 / M54 adapter for camera
- 1x Soft padded carrying case
Special Limited Edition - Limited to stock on hand only
- An internal focusing design moves the lens elements inside the tube rather than racking a heavy drawtube out the back, eliminating camera tilt, flexure, and vignettes while remaining fully compatible with electronic focusers like the ZWO EAF
- A premium 5-element Petzval design natively corrects and illuminates up to Medium Format sensors with tack-sharp stars from corner to corner—no external field flattener required
- Stepping up to a larger 91mm aperture and a versatile 448mm focal length (f/4.9), it delivers far more light-gathering muscle and deep-sky reach than smaller RedCat models
William Optics RedCat 91 WIFD: A Beast in the RedCat Lineup
Introducing the William Optics RedCat 91 WIFD sleek Space Grey refractor. Built around a groundbreaking 5-element advanced Petzval optical design, the RedCat 91 expands on the iconic portable refractor series that astrophotographers of all skill levels have raved about for years. This limited-edition powerhouse brings a significantly larger 91mm aperture and a deeper 448mm focal length to the table, providing the extra light-gathering muscle and reach you need for faint deep-sky targets while maintaining the signature, pinpoint, flat-field star quality the series is famous for.
More than just a focal length upgrade, the RedCat 91 is an engineering masterpiece. It features William Optics' patented WIFD (William's Internal Focusing Design) system, meaning the focuser draws internally to completely eliminate heavy camera tilt and vignette issues while maintaining electronic focus compatibility (like the ZWO EAF) straight out of the box. This refractor comes with essentail tools like a multi-functional handle, built-in Bahtinov mask lens cap and a camera angle rotator; all while effortlessly illuminating up to a 55mm image circle (Medium Format). It’s not just a giant leap forward in wide-field imaging performance—it’s a stunning piece built for the next generation of astrophotography.
Full Frame Image Circle & Pinpoint Corner Stars
The RedCat 91 features 5 total lens elements, arranged in what William Optics calls an "advanced Petzval design" (consisting of 2 "super" ED (SD), 1 ED, 1 lanthanum and 1 undisclosed element lenses). This results in a huge 55mm image circle, which is not just full frame compatible, but nearing medium format sensor territory. We strongly recommend checking out the spot diagram below — note how small the spot sizes are even at a radius of 21.6mm (bottom right chart), which is where the stars would be in the corners of a full frame sensor
WIFD Focuser: EAF Compatible
The RedCat 91 features the same high-quality focuser in the rest of the RedCat line, William Optics' patented William Optics Internal Focus Design (WIFD) focuser. This innovative focuser design moves the focus drawtube and lens elements all internally. This has a number of large benefits for astrophotographers.
First and foremost, it can support heavy image trains with large filter wheels, cameras, and rotators without introducing any tilt, though a tilt adapter is still included just in case. Second, any vignetting caused by the focuser is eliminated due to the design. Third, because the drawtube is entirely internal, the telescope's overall length does not change when changing focus. Simply put, the WIFD is one of the best focuser designs available in consumer telescopes. It is also compatible with third-party electronic focusers like the ZWO EAF out of the box.
Portability & Soft Travel Case Included
Weighing just 14 lbs (6.3 kg) total with the included tube rings and dovetail plate, the RedCat 91 remains incredibly portable and is small enough to fit in a standard overhead carry-on bag. A soft carry case is included, keeping your RedCat 91 safe & protected during any type of travel.
RedCat 91 Focal Length, Aperture, and Focal Ratio
The RedCat 91's focal length is 448mm, which makes it perfect for photographing medium focal length reach targets like large galaxies and nebulae. The aperture as the name implies is 91mm, which is a significant step up over the RedCat 51, 61, and 71. This larger aperture allows for capturing higher resolution on detailed objects. Lastly, the RedCat 91's focal ratio is f/4.9, which is the same fast focal ratio found on the rest of the RedCat line.
Specifications
-
Lens Type: 5-element Petzval design
-
Aperture: 91 mm (3.58 in)
-
Focal Length: 448 mm
-
Focal Ratio: f/4.9
-
Glass Elements: 2 x Super ED, 1 x ED, 1 x Lanthanum, 1 x Undisclosed Element
-
Image Circle: 50 mm (Full-Frame and Medium Format coverage)
-
Camera Format Support: Medium Format (requires optional adapter), Full Frame, APS-C, Micro Four Thirds (M4/3)
-
T-Mount Compatibility: Canon EF/RF, Nikon F/Z, Sony E, Pentax K, Micro Four Thirds (M4/3), FUJI X
-
Focuser Type: WIFD Rack & P inion focuser (ZWO EAF electronic focuser compatible)
-
Focuser Travel: 36 mm (features 0–40 mm physical mark ings)
-
Focuser Features: Focus lock knob and integrated thermometer scale
-
Maximum Backfocus (with M48 Adapter): 60.8 mm (2.39 in)
-
Maximum Backfocus (with M54 Adapter): 65.8 mm (2.59 in)
-
Rear-End Mechanical Adapters: integrated camera tilt adjuster, field rotator, M63-to-M54 adapter, and M63-to-M48 adapter
-
OTA Weight (Tube Only): 4.72 kg (10.41 lb)
-
Total instrument Weight: 6.30 kg (13.89 lb) ( includes dual mount ing r ings and large dovetail plate)
-
Total Optical Tube Length: 556 mm (21.89 in)
-
Ma in Tube Outer Diameter: 116.5 mm (4.59 in)
-
Dew Shield Outer Diameter (OD): 120 mm (4.72 in)
-
Dew Shield inner Diameter (ID): 117 mm (4.61 in)
-
Dew Shield Length: 180 mm (7.09 in)
-
Rigging & Mounting: 290 mm (11.42 in) Vixen-style bottom dovetail plate; top multi-functional saddle handlebar
-
Finderscope Mount: Bracket and saddle bar included
- Color: Space Grey finish
Other Information
- Country of Manufacture: Taiwan
| Manufacturer | William Optics |
|---|---|
| Telescope Focal Length | 401 - 500mm |
- 1x RedCat 91 - Space Gray
- 1x Dust cover w/ bahtinov mask
- 1x Saddle handlebar
- 1x Tube rings
- 1x Camera angle rotator
- 1x Tilt adapter
- 1x 290mm Vixen-style dovetail plate
- 1x M63 to M48 / M54 adapter for camera
- 1x Soft padded carrying case