CThe William Optics Cat 91 f/4.9 is a 5 element (3 of which are ED elements) Petval design refractor with stunning all black anodized finish, compact optical design for travel ease with exceptionally high quality optics and now includes the innovative WIFD internal focus design.  

At the heart of this groundbreaking design lies the patented William Optics center focuser, seamlessly integrated with the internal focuser mechanism to achieve an ingenious synergy. Through the precise manipulation of the telescope's fixed optics, the Internal Focus Design (WIFD) enables effortless and accurate adjustments to the focus, delivering unmatched clarity and sharpness in every captured moment. Moreover, the internal focuser acts as a fortress, providing exceptional protection to the delicate optics, shielding against misalignment and ensuring unwavering performance under any circumstances.

A standout advantage of the WIFD lies in its remarkable ability to distribute the weight of the imaging system evenly, resulting in heightened stability during captivating astrophotography sessions. This harmonious weight distribution alleviates strain on the telescope mount, minimizing the occurrence of disruptive vibrations and granting the freedom to extend exposure times without compromising the pristine quality of the captured images. With the user-friendly rack and pinion focuser, astronomers can effortlessly fine-tune focus adjustments, offering unparalleled command over capturing their desired celestial subjects. Complementing this precision is an easily readable graduated display, serving as an intuitive aid that streamlines the process of achieving meticulous focus.

The integration of the patented William Optics center focuser and the internal focuser mechanism represents a leap forward in optical innovation. By harmonizing their capabilities, the WIFD system delivers not only exceptional clarity and protection but also enhanced stability and control, enabling astronomers to delve into the depths of the cosmos with unmatched confidence and finesse.

• Lens Type: Petzval Design
• Aperture: 91mm
• Focal Ratio: f/4.9
• Image Circle 50mm
• Flattener: Petzval Flat Field
• Focuser: WIFD Internal Focus Design, Compatible with EAF
• Lens Material: FPL-53
• Camera Format Compatibility: Full Frame, DSLR, Mirrorless, CMOS and CCD
• T-Mounts Supported: Canon EF, RF, NIkon F, Z, Sony E, Pentax K, Micro Four Thirds, FUJI X
• Tube Length: 556mm
• OTA Weight: 10.41 lbs.
• Total System Weight: 13.89 lbs.