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SKU: T-C-91

Cat 91 WIFD

$2,998.00 USD Tax Included

$2,338.00 USD before tax and duties. Tax and duties will be collected during checkout.

⛟ Free Shipping Free shipping on orders over $498. Import charges not included.
Description
Description

Step up your astrophotography game with the William Optics RedCat 91, an advanced apochromatic refractor tailored for full-frame and medium-format cameras. This latest addition to the RedCat series combines portability with superior optical performance, making it a versatile tool for capturing breathtaking detail in deep-sky objects.

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 RedCat 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 RedCat 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 RedCat 91 provides precise, stable focusing without additional adjustments, enhancing the ease of use for both seasoned astrophotographers and beginners.

The RedCat 91 blends the trusted RedCat heritage with William Optics’ innovative design, making it the ultimate choice for those ready to elevate their night-sky explorations.

Notice
Notice

Astrophotography Only
This telescope is specifically designed for astrophotography, and its optical design does not support visual observation.

Color:Black

Pairs well with


Cat 91 WIFD
Cat 91 WIFD Sale price$2,338.00 USD Tax excluded.

What's in the box

Main Tube

Bahtinov Cap

M48, M54
Camera Adapter

Vixen-style Plate

Mounting Ring & Handle bar

Riser Blocks

Soft Carry Case

Allen Key Set

The cat with medium-format soul

An advanced apochromatic refractor tailored for full-frame and medium-format cameras. This latest addition to the RedCat series combines portability with superior optical performance, making it a versatile tool for capturing breathtaking detail in deep-sky objects.


Advanced Petzval

Researched and developed by WO, the innovative 5-element Petzval design redefines telescope optics. This advanced system achieves a flawless spot diagram across a medium-format image circle.

Extra-low Dispersion (ED) glasses

Contains 2 Super ED, 1 ED glasses and lanthanum lenses with advanced fully multi-coated, delivering sharp, vibrant images with true-to-life colors, significantly reducing chromatic aberration.

Needs NO Flattener

The Petzval design inherently flattens the field, eliminating the need for an external field flattener.

Never easier to capture deep sky objects

UC91 - Clamshell - Jonathan

Sh2 119 - The Clamshell Nebula

Jonathan

UC91 - Corona - Daemon de Chaeney

Corona Australia Molecular Cloud & NGC 6723

Daemon de Chaeney

UC91 - HorseHead - Mehmet Ergün

M20 & M8 Wide Field

Mehmet Ergün

UC91 - NGC2237 - Reynold Edwards

NGC 2237 Rosette

Reynold Edwards

UC91 - NGC224 - Reynold Edwards

Andromeda

Reynold Edwards

UC91 - Omega - Jakub Korbel

Omega Centauri

Jakub Korbel

UC91 - Ophiuchi - Jakub Korbel

Rho Ophiuchi Region

Jakub Korbel

UC91 - Clamshell - Jonathan

Sh2 119 - The Clamshell Nebula

Jonathan

UC91 - Corona - Daemon de Chaeney

Corona Australia Molecular Cloud & NGC 6723

Daemon de Chaeney

UC91 - HorseHead - Mehmet Ergün

M20 & M8 Wide Field

Mehmet Ergün
UC91 - NGC2237 - Reynold Edwards

NGC 2237 Rosette

Reynold Edwards

UC91 - NGC224 - Reynold Edwards

Andromeda

Reynold Edwards

UC91 - Omega - Jakub Korbel

Omega Centauri

Jakub Korbel

UC91 - Ophiuchi - Jakub Korbel

Rho Ophiuchi Region

Jakub Korbel

Compatible with Electronic Motorized Devices

Hassle Free Installation
( No Mounting Bracket Kit required )

Leading the market

Wo patented design

The Cat 91 holds three unique patents, ensuring easy and perfect focusing along with precise coaxial image quality, preventing draw tube tilt issues caused by optical misalignment.

:

Internal Focuser

The WIFD focusing design relocates the focuser to the center of the telescope, eliminating tube tilt caused by the weight of cameras and accessories. By removing the need for a traditional rear drawtube, the optical path remains fully unobstructed, ensuring clean and precise image performance.

Integrated Bahtinov mask

Laser engraved on high-definition and stable optical PMMA. Enhances astrophotography experience with quick and accurate adjustments.

CAT Handle Bar

Crafts for enhanced portability and versatility.

Mounting Ring

Designed for seamless functionality without compromising on stability. Engineered with wide surface contacts, this innovative ring ensures a secure fit while enabling fast, easy detachment.

comprehensive configuration

Precision Imaging Adjustment

Tilt Adjuster

The built-in tilt adjuster makes it easy to correct camera sensor tilt issues.

Camera Angle Rotator

Correct any angular discrepancies, and get the perfect angle on your images.

Gallery

Swipe left and right to view the Original & After processed image.

Original

After Process

Use the left and right arrow keys to navigate between before and after photos.

▲ IC434 (APS-C)

Cat 91 + ZWO ASI 2600MC Duo
Courtesy of Mehmet Ergün

  1. Stacked ( Original & After Process )
  2. Original Single Shot Corner Grid

▲ M45 (Full-Frame)

Cat 91 + ZWO ASI 6200MC Pro
Courtesy of Dear Bear

  1. Stacked ( After Process )
  2. Original Single Shot Corner Grid

Reviews

William Optics RedCat 91 Review

I recently tested the William Optics RedCat 91 APO refractor. This is the fourth RedCat I’ve used in the RedCat series—five if you count the two versions of the RedCat 51 (version 1 and version 3).
With a healthy aperture, fast optics, and a super flat Peztval design, the William Optics RedCat 91 has a lot going for it. It includes several thoughtful features, such as a tilt adjuster, a camera angle rotator, and a robust WIFD focuser.
This telescope has two color options: the classic red and a new black version. William Optics sent me the black one and explained that it’s one of the best telescopes he’s ever produced.