William Optics Telescopes & Accessories

William Optics specializes in premium refractor telescopes and accessories for amateur astronomers and astrophotographers. Since 1996, founder William Yang has built the Taiwan-based company into a respected name in the astronomy community. William Optics scopes stand out for elegant styling, quality materials, and robust focusers.

In any refractor, the most important component is the glass. Every William Optics refractor uses extra-low dispersion (ED) glass, including their doublet refractors. ED glass produces sharp, color-correct views of celestial objects, so even entry-level models can deliver impressive results. Whether you are capturing your first wide-field images or building a dedicated astrophotography rig, you can find a William Optics telescope and accessories to match your goals at Agena Astro.

William Optics has fully embraced the classic Petzval refractor design, making astrophotography simpler and more streamlined. These compact imaging refractors feature built-in field flatteners, eliminating the need for separate correctors or precise spacer tuning. That means less time calculating back-focus and fewer accessories to buy—often you can attach your camera, reach focus, and start imaging. Models equipped with the internal WIFD focuser take it even further, positioning the focuser inside the optical tube to help minimize camera sensor tilt for more consistent stars across the frame.

Compact and travel-friendly, William Optics Petzvals are especially well-suited for wide-field imaging at dark-sky sites. The lineup ranges from classic four-element designs to advanced multi-element astrographs with integrated focal reduction for faster systems and large-sensor performance.

Popular William Optics Petzval Refractors:

• RedCat 51
• RedCat 71
• Pleiades 68
• UltraCat 108

William Optics manufactures apochromatic (APO) triplet refractors with excellent color correction. The classic three-element design greatly reduces false color, including when imaging bright targets, and it typically outperforms doublet designs in this regard. Models range from entry-level like the GT71 71mm, to premium choices like the Fluorostar 132mm f/6.9. William Optics triplet refractors come in a variety of apertures, focal ratios, and finishes.

For astrophotography, triplet refractors perform best when paired with the correct field flattener or focal reducer. For visual astronomy, they provide crisp, high-contrast views with minimal chromatic aberration. This makes them well suited for deep-sky imaging and planetary observing.

William Optics doublet refractors strike an excellent balance between performance and price. These scopes typically use a single ED element to control chromatic aberration, making them a versatile choice for both imaging and visual observing. Many models include dual-speed focusers for precise fine adjustments—especially helpful when dialing in critical focus with a camera.

For imaging, doublet refractors generally require a dedicated field flattener or focal reducer to maintain sharp stars across the entire field, and these accessories specify proper back-focus spacing. For visual use, setup is simple—a diagonal and eyepiece are often all you need to begin observing.

Popular William Optics Doublets:

• Zenithstar 61

• Zenithstar 81

William Optics offers field flatteners and focal reducers matched to telescope lines that need them. These accessories correct the naturally curved focal plane of a refractor, helping keep stars sharp from center to edge. Many models also reduce focal length, which provides a wider field of view and a faster effective focal ratio.

The accessory lineup includes both scope-specific and more universal options. Some flatteners also use low-dispersion glass to help preserve color correction through the full optical train without sacrificing image quality or sharpness.

William Optics offers multiple sizes and styles of guide scopes and finder scopes. These mount to tube rings and finder bases on many William Optics telescopes, as well as on compatible third-party systems. Guide scopes provide clear star images for accurate autoguiding during long exposures.

Many designs use lightweight housings and mount via Vixen-style rails or standard finder bases. Premium guide scopes typically use standard 1.25-inch openings, making them compatible with most guide cameras. William Optics also makes red-dot finders and magnifying finder scopes to make alignment quick and straightforward.

William Optics produces premium mirror and prism diagonals for visual observing. High-reflectivity coatings help maximize light transmission across a wide range of eyepieces. Many diagonals include secure attachment collars with a rotary locking mechanism for a stable, repeatable connection.

This locking style is also used on select adapters and extensions, helping support both visual accessories and imaging trains. In addition to standard diagonals, William Optics offers erecting prisms for terrestrial viewing and for specific lunar observing applications.

William Optics tube rings are designed to match their telescopes, but many will also fit other brands with a compatible outer tube diameter. Rings are machined from aluminum for strength and low weight, and they are available in multiple finishes. Options include full-size rings for main optical tubes and smaller 50 mm rings for finders and guide scopes.

Full-size rings often include multiple mounting points for accessories and for William Optics handlebars. William Optics also offers standard dovetail bars and dual-sided dovetail plates compatible with both Vixen and Arca-Swiss systems. Additional accessories include T-ring adapters for major camera brands such as Canon, Nikon, Sony, and Fujifilm, including models with extra-wide M48 threads for full-frame cameras.