William Optics WIFD Ultra-Cat 131 APO Refractor
William Optics WIFD Ultra-Cat 131 APO Refractor
Looking to push your astroimaging experience to the next level? Check out this power-packed William Optics Ultra-Cat 131 APO, a telescope built for serious astrophotography performance. The five internal optical elements present tack-sharp stars and exceptional color correction across the entirety of medium-format sensors, while the large 131 mm (5.16”) aperture collects a copious amount of light for outstanding brightness and resolution of detail. Petzval in design, there is no need for an additional field flattener nor backspace calculation. Quality-crafted and designed with imaging excellence in mind, precision-driven astroimagers are sure to be delighted by this stellar scope!
This 131 mm Ultra-Cat is the largest model within this elite William Optics series, and a refractor this size means one thing: incredible brightness within your frames! Stunning detail on a plethora of cosmic wonders is yours for the taking thanks to its large aperture and 648 mm focal length. The substantial scale of this refractor continues with its image circle, delivering 60 mm in diameter of edge-to-edge sharpness that users of medium-format sensors are sure to appreciate. In addition to these superior optics, this apochromatic telescope comes furnished with the William Optics Internal Focus Design (WIFD) for smooth, stable focusing. Effortlessly add an electronic autofocuser when pairing your scope with the specialty EAF adapter kit from William Optics (EAF and specialty bracket not included) for automatic, hands-free focusing. An outstanding refractor in all instances, the William Optics Ultra-Cat 131 is a standout choice for astroimagers seeking powerful, next-level performance.
A Quintuplet Powerhouse
The five internal lenses within this William Optics Ultra-Cat 131 refractor are meticulously aligned to deliver top-notch quality. As incoming light passes through each lens, the light rays converge with extreme precision, eliminating chromatic aberration, field curvature, and any other optical distortions! Built-in flat-field correction means there is no need for an external field flattener, streamlining your setup. Additionally, there’s no need to calculate backfocus. As long as you can reach focus, the entire 60 mm image circle will be in focus as well! This ready-to-go refractor offers use right out of the box, helping you spend more time imaging the stars and less time fumbling with gear configurations. With these outstanding optics, breathtaking images of our universe are right at your fingertips.
Remarkable Deep-Sky Imaging Performance
Backed by over 5” of aperture and 648 mm of focal length, you’re well equipped for near limitless imaging possibilities. Fill the entire frame with colorful nebulosity when aimed at the Orion or Sagittarius constellations, or hone in on smaller objects like the Dumbbell Nebula, the Iris Nebula, or the Ghost of Cassiopeia. When paired with a crop sensor camera, some of the planets are yours for capture as well! Be stunned by Saturn’s rings, the ice caps on Mars, and the stormy clouds on Jupiter. The fast focal ratio of f/4.9 gives way to bright images in little time, and three rear-end adapters come standard with this Ultra-Cat 131 (M48, M54 and M68) for effortless camera attachment.
WIFD Focuser Design with EAF Compatibility
Instead of moving your imaging train forwards and backwards to find focus, this William Optics Ultra-Cat 76 APO refractor houses an internal focuser, moving the optics internally to find focus instead. By holding your imaging train steady, the possibility of drawtube sag is greatly diminished, especially for heavier imaging equipment. This also reduces the chance of any vignetting due to drawtube instability, resulting in higher image quality. If you’d like to automate your focusing routine, this focuser is also EAF ready!
Included Sensor Tilt Xterminator
Helping you maximize your image quality by eradicating tilt, William Optica includes their innovative Sensor Tilt Xterminator with your Ultra-Cat 56! This handy tool improves upon the original 4 pull-in and 8 push-out screw configuration, simplifying it to a more efficient 4 push-out and 4 locked screw system. “Seesaw-style”, this accessory makes it easy to quickly adjust any present tilt without having to remove your camera. Simply loosen one screw and tighten the opposing diagonal screw until proper alignment is reached.
The Complete Package
In addition to the Sensor Tilt Xterminator, William Optics includes a variety of additional accessories within this package! The signature William Optics dual-use objective cap/Bahtinov mask is a handy tool, providing both protection for your optics as well as a simple method of finding perfect focus. Further assisting with focus, you’ll find a focusing scale and temperature gauge on the coarse focusing knob. These thoughtful features enable quick returns to previous focusing positions and precise monitoring of nighttime temperature shifts. Atop the handle bar, easily add accessories such as a guidescope or a WiFi camera control device. A set of M4 screw holes on the side of this telescope offer attachment of a user-supplied finder base for additional accessory mounting! For addition of a user-supplied finder base, M4 screw holes can be found on the side of this telescope. The dual-use handle bar enables attachment of extra accessories as well! Also included are mounting rings to keep your refractor secure, and a Losmandy-style dovetail plate.