RedCat 91 WIFD arrives from William Optics

William Optics has announced the launch of the RedCat 91 WIFD, an advanced apochromatic refractor telescope designed to elevate the astrophotography experience for both amateurs and professionals. This latest addition to the esteemed Cat series combines cutting-edge optical performance with innovative design features, setting a new standard in the field."The cat with medium format soul" as William Optics puts it, is a scope tailored for full-frame and medium-format cameras.

Oh - also, don't worry "RED" cat people, it comes in red and black (your choice).

I currently own the first-generation RedCat 51 and RedCat 71, and the release of the 91 WIFD has me seriously contemplating whether now is the perfect time to upgrade. One of my all-time favorite astrophotos, the wide-field Orion complex region, was captured with my RC 51, showcasing its incredible performance. It’s a reminder of how much these scopes have shaped my astrophotography journey.

Key Features of the RedCat 91 WIFD:

• Advanced Petzval Design: The RedCat 91 WIFD boasts a 5-element Petzval optical system, including three Super Extra-low Dispersion (ED) glasses. This configuration ensures sharp, vibrant images with true-to-life colors and significantly reduces chromatic aberration. The inherent field-flattening capability eliminates the need for an external field flattener, simplifying the imaging process.

• Internal Focusing Mechanism (WIFD): Incorporating William Optics' patented Internal Focus Design (WIFD), the focuser is centrally located within the telescope. This design addresses issues of tube tilt caused by the weight of accessories and cameras, providing a balanced structure with superior rigidity. The precise internal sliding of fixed optics prevents image shift, ensuring stable and clear observations. 

• Compatibility and Versatility: With a 55mm image circle, the RedCat 91 WIFD is suitable for full-frame and medium-format cameras. The telescope includes a built-in tilt adjuster and camera angle rotator, allowing users to correct sensor tilt issues and achieve the perfect angle for their images. The M48 thread at the end of the telescope ensures compatibility with various camera adapters. 

• Enhanced User Experience: The integrated Bahtinov mask, laser-engraved on high-definition and stable optical PMMA, facilitates quick and accurate focusing adjustments. The telescope's design also includes a handle bar with a mini Vixen-style mounting base, enhancing portability and versatility. 

Availability:

The RedCat 91 WIFD is now available for pre-order, with shipments commencing in one week. Early adopters will receive a complimentary UniGuide 32mm f/3.75 guide scope, valued at $114. 

 

Technical Specifications of the RedCat 91 WIFD

Optical System:
The CAT 91 WIFD boasts a 5-element Advanced Petzval design, featuring:

Two Super ED Glass Elements: Minimize chromatic aberration for vivid, color-accurate imaging.
One ED Glass Element: Enhances light transmission and clarity.
One Lanthanum Glass Element: Reduces residual dispersion, ensuring pinpoint star resolution.
One X-Element: Delivers exceptional sharpness across the entire field of view.

Focal Length & Ratio:
448 mm focal length and a fast f/4.9 focal ratio, making it ideal for capturing wide-field images of nebulae, star clusters, and galaxies.

Image Circle:
A generous 55 mm image circle, supporting medium format, full-frame, and APS-C cameras, with perfect edge-to-edge flatness.

Integrated Internal Focus Design (WIFD):
The patented rack-and-pinion WIFD system ensures precise and stable focusing without external image shift. Compatible with electronic automatic focusers (EAF), the WIFD system maintains rigidity even with heavy imaging setups.

Camera Compatibility:
The CAT 91 WIFD supports a wide range of camera mounts, including:

Canon EF, RF
Nikon F, Z
Sony E
Pentax K
Micro Four Thirds (MFT)
Fujifilm X

No Flattener Needed:
The optical system’s native flat field eliminates the need for an external field flattener, simplifying imaging setups.

Mechanical Design:
Tilt Adjuster Rotator: Correct sensor alignment and adjust the camera angle effortlessly.
Adapters Included: M63 → M54 and M63 → M48 adapters, ensuring compatibility with various setups.

Dimensions and Weight:
Tube Length: 556 mm
OTA Weight: 4.72 kg (10.41 lbs)
Total Weight (with accessories): 6.3 kg (13.89 lbs)

Comparison with Other Telescopes in Its Class

The CAT 91 WIFD stands out among similar refractors, such as the Takahashi FSQ-85 and the SharpStar 94EDPH, in several key areas:

1. Optical Design:
   While many competitors rely on 4-element designs, the CAT 91 WIFD’s 5-element Advanced Petzval system offers superior chromatic correction and edge-to-edge sharpness without requiring an external field flattener.

2. Focal Ratio:
   Its f/4.9 ratio is faster than the FSQ-85’s f/5.3, making it more suitable for wide-field astrophotography and shorter exposure times.

3. Integrated WIFD Focuser:
   The innovative WIFD system reduces potential issues with tube flexure, a common challenge with external focusers, providing a level of stability unmatched by most telescopes in its class.

4. Image Circle Size:
   The CAT 91 WIFD’s 55 mm image circle accommodates medium-format cameras, a feature often missing in its competitors.

5. Weight and Portability:
   At 4.72 kg (10.41 lbs), the CAT 91 WIFD is lightweight and compact, ideal for field use, and pairs well with portable astrophotography rigs.

Who Is It For?

The RedCat 91 WIFD is an excellent choice for:

• Astrophotographers looking for a compact yet powerful telescope for wide-field imaging.
• Traveling enthusiasts requiring a lightweight, portable design.
• Professional and amateur astronomers seeking unparalleled optical performance without additional accessories like flatteners.
  
   

Should I upgrade? Light Grasp Comparisons between the 51, 71, and 91

The light grasp of a telescope is directly related to the aperture, or the diameter of the telescope's primary lens or mirror. Light grasp determines how much light the telescope collects, which in turn affects its ability to resolve faint objects. The larger the aperture, the more light the telescope can collect.

To calculate the light grasp, we compare the apertures of the telescopes by squaring their diameters, as the area of the lens or mirror is proportional to the square of its diameter:

1. RedCat 51 (51mm Aperture):
   Light grasp proportional to 51 (squared) = 2,601
   Baseline for comparison.

2. RedCat 71 (71mm Aperture):
   Light grasp proportional to 71 (squared) = 5,041
   Collects 5,041/2,601≈1.945,041/2,601 ≈ 1.94 times more light than the RedCat 51.

3. RedCat 91 WIFD (91mm Aperture):
   Light grasp proportional to 91 (squared) = 8,281
   Collects 8,281/2,601≈3.188,281/2,601 ≈ 3.18 times more light than the RedCat 51.
   Collects 8,281/5,041≈1.648,281/5,041 ≈ 1.64 times more light than the RedCat 71.

Practical Implications for Astrophotography

• RedCat 51: Ideal for wide-field imaging of bright objects like large nebulae (e.g., Orion) due to its compact size and lower light grasp. But as Kay Ogetay demonstrated - the RC51 is more than capable.
   
• RedCat 71: Offers nearly double the light grasp of the 51mm, allowing for more detail and slightly deeper imaging of dimmer targets while still maintaining a relatively wide field of view.
   
• Cat 91 WIFD: With more than triple the light grasp of the 51mm, the 91mm aperture enables capturing significantly fainter objects and finer details, especially useful for galaxies, clusters, and complex nebulae structures. The added light collection also means shorter exposure times for equivalent results compared to the smaller apertures.
  
  In essence, upgrading to the 91 WIFD would be a leap in capability, especially for imaging faint deep-sky objects, while still retaining the high optical quality associated with the RedCat line.

 

William Optics RedCat 91: First Look

Order the RedCat 91 Right Here