William Optics RedCat 91 WIFD f/4.9 Petzval Refractor Telescope (Black with Red Trim)
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A Beast in the RedCat Lineup
Introducing the new William Optics RedCat 91! This 5-element Petzval refractor is the latest telescope in William Optics' highly-reviewed RedCat line. Astrophotographers of all skill levels have raved about the RedCat series of telescopes for years for being portable, affordable, and superior optical performance. The RedCat 91 continues this legacy but with a longer focal length and larger aperture.
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:
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.
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 Specifications
- OTA Weight：4.72kg / 10.41lbs
- Total Weight：6.30kg / 13.89lbs (includes two rings and large dovetail plate)
- Total Length: 556mm
- Lens Type: 5 element Petzval design
- Focal Length: 448 mm
- Diameter: 91 mm (2 x Super ED, 1 x ED, 1 x Lanthanum, 1 x undisclosed element)
- Aperture: f/4.9
- Image circle: 50mm
- Focuser: WIFD R&P focuser compatible with EAF
- Focuser travel: 36mm (0-40mm mark)
- Focuser knob: Yes, with lock, thermometer scale
- Finderscope: Bracket, saddle bar only
- Maximum available back focus with M48 adapter: 60.8mm
- Maximum available back focus with M54 adapter: 65.8mm
- Rear end adapters: Tilt, rotator, M63-M48, M54
- Dew shield OD: 120mm
- Dew shield ID: 117mm
- Dew shield length: 180mm
- Tube diameter: 116.5mm
- Total tube length: 556mm
- Dovetail bar: 290mm Vixen style plate (bottom), saddle handle bar (top)
- Soft Carrying Case
- Box weight: 22lbs 4oz, 10.10kg
- Free 32mm William Optics guidescope and hex key set.
Other Information
- Country of Manufacture: Taiwan
A Beast in the RedCat Lineup
Introducing the new William Optics RedCat 91! This 5-element Petzval refractor is the latest telescope in William Optics' highly-reviewed RedCat line. Astrophotographers of all skill levels have raved about the RedCat series of telescopes for years for being portable, affordable, and superior optical performance. The RedCat 91 continues this legacy but with a longer focal length and larger aperture.
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:
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.
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 Specifications
- OTA Weight：4.72kg / 10.41lbs
- Total Weight：6.30kg / 13.89lbs (includes two rings and large dovetail plate)
- Total Length: 556mm
- Lens Type: 5 element Petzval design
- Focal Length: 448 mm
- Diameter: 91 mm (2 x Super ED, 1 x ED, 1 x Lanthanum, 1 x undisclosed element)
- Aperture: f/4.9
- Image circle: 50mm
- Focuser: WIFD R&P focuser compatible with EAF
- Focuser travel: 36mm (0-40mm mark)
- Focuser knob: Yes, with lock, thermometer scale
- Finderscope: Bracket, saddle bar only
- Maximum available back focus with M48 adapter: 60.8mm
- Maximum available back focus with M54 adapter: 65.8mm
- Rear end adapters: Tilt, rotator, M63-M48, M54
- Dew shield OD: 120mm
- Dew shield ID: 117mm
- Dew shield length: 180mm
- Tube diameter: 116.5mm
- Total tube length: 556mm
- Dovetail bar: 290mm Vixen style plate (bottom), saddle handle bar (top)
- Soft Carrying Case
- Box weight: 22lbs 4oz, 10.10kg
- Free 32mm William Optics guidescope and hex key set.
- Optical Tube Assembly
- Dust cover with bahtinov mask
- Saddle handlebar
- Tube rings
- Camera angle rotator
- Tilt adapter
- 290mm Vixen-style dovetail plate
- M63 to M48 / M54 adapter for camera
- Carrying case
A Beast in the RedCat Lineup
Introducing the new William Optics RedCat 91! This 5-element Petzval refractor is the latest telescope in William Optics' highly-reviewed RedCat line. Astrophotographers of all skill levels have raved about the RedCat series of telescopes for years for being portable, affordable, and superior optical performance. The RedCat 91 continues this legacy but with a longer focal length and larger aperture.
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:
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.
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 Specifications
- OTA Weight：4.72kg / 10.41lbs
- Total Weight：6.30kg / 13.89lbs (includes two rings and large dovetail plate)
- Total Length: 556mm
- Lens Type: 5 element Petzval design
- Focal Length: 448 mm
- Diameter: 91 mm (2 x Super ED, 1 x ED, 1 x Lanthanum, 1 x undisclosed element)
- Aperture: f/4.9
- Image circle: 50mm
- Focuser: WIFD R&P focuser compatible with EAF
- Focuser travel: 36mm (0-40mm mark)
- Focuser knob: Yes, with lock, thermometer scale
- Finderscope: Bracket, saddle bar only
- Maximum available back focus with M48 adapter: 60.8mm
- Maximum available back focus with M54 adapter: 65.8mm
- Rear end adapters: Tilt, rotator, M63-M48, M54
- Dew shield OD: 120mm
- Dew shield ID: 117mm
- Dew shield length: 180mm
- Tube diameter: 116.5mm
- Total tube length: 556mm
- Dovetail bar: 290mm Vixen style plate (bottom), saddle handle bar (top)
- Soft Carrying Case
- Box weight: 22lbs 4oz, 10.10kg
- Free 32mm William Optics guidescope and hex key set.
Other Information
- Country of Manufacture: Taiwan
| Free Shipping Graphic | Free Contiguous US Shipping |
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| Telescope Focal Length | 401 - 500mm |
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- Optical Tube Assembly
- Dust cover with bahtinov mask
- Saddle handlebar
- Tube rings
- Camera angle rotator
- Tilt adapter
- 290mm Vixen-style dovetail plate
- M63 to M48 / M54 adapter for camera
- Carrying case
William Optics RedCat 91 WIFD f/4.9 Petzval Refractor Telescope (Black with Red Trim)