William Optics RedCat 91 WIFD f/4.9 Petzval Refractor Telescope - Black

William Optics RedCat 91 WIFD

The William Optics RedCat 91 WIFD is a new addition to WO's range of fast Petzval refractors with their innovative internal focusing mechanism. This makes it simple to install autofocusers such as the ZWO EAF without the need for clumsy belt-driven add-ons.

Full Frame Image Circle & Pinpoint Corner Stars

The RedCat 51 series has kept one thing constant: the f/4.9 focal ratio. This all changes with the MiniCat 51. It now features a blazing fast f/3.5 focal ratio, meaning it can gather the same amount of light in less than half the time as the RedCat 51!

This faster focal ratio lets you focus more on capturing your target in staggering detail. Of course with the focal ratio change also comes a change in focal length: the focal length is reduced from 250mm down to 178mm. This focal length is ideal for capturing large widefield views of the night sky.

Same Full Frame Image Circle

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.

Integrated Bahtinov Mask

The patented bahtinov mask is laser engraved on high definition and stable optical PMMA and enhances astrophotography experience with quick and accurate adjustments.

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.

The WIFD focuser design relocates the focuser to the center of the telescope, addressing the issue of tube tilt caused by the weight of accessories and cameras.

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.

William Optics 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.