The ZWO 90mm f/6.8 Quadruplet APO Refractor is a compact, imaging-focused telescope designed to deliver sharp, wide-field views of nebulae, star clusters, and expansive deep-sky targets. Its 609mm focal length provides a versatile balance between field of view and image scale, while the four-element apochromatic optical design produces well-corrected stars across the entire frame without requiring a separate field flattener, simplifying both setup and backfocus spacing. A generous fully corrected imaging system supports modern astronomy cameras, making it well-suited for a wide range of sensor formats.

Lightweight and travel-friendly for its aperture class, the 90mm APO pairs naturally with portable mounts such as the ZWO AM3N and AM5N, making it an excellent choice for mobile astrophotography setups. The dual-speed 3" rack-and-pinion focuser provides smooth, precise focusing control, enabling fine adjustments essential for high-resolution imaging. With its robust build and imaging-ready design, it integrates easily into both beginner and advanced astrophotography systems.

With a 90mm aperture and 609mm focal length at f/6.8, the ZWO 90mm APO strikes a strong balance between portability, resolution, and light-gathering performance. The optical tube weighs just under 10 lb, making it manageable for modern harmonic drive and lightweight equatorial mounts while still providing increased capability over smaller aperture refractors.

Designed with versatility in mind, the 90mm APO adapts seamlessly to a wide range of astronomical applications. It offers straightforward compatibility with dedicated astronomy cameras, DSLRs, and mirrorless cameras, making it suitable for both newcomers building their first serious imaging rig and experienced astrophotographers expanding their setup. With optional accessories, it can also be configured for visual observing, functioning as a capable refractor for both imaging and visual use.

Its native flat-field quadruplet optical design eliminates the need for a separate field flattener, simplifying the imaging train and reducing setup complexity. Without the need for precise backfocus calculations or spacing adjustments, users can spend less time configuring equipment and more time capturing the night sky.

The FF90 APO utilizes a four-element, fully air-spaced apochromatic optical design that delivers a naturally flat imaging field without requiring an additional field flattener. By integrating all four optical elements into the design, the telescope produces sharp, well-corrected stars across the frame while simplifying the imaging train. An extra-low dispersion (ED) glass element helps minimize chromatic aberration, improving color accuracy and contrast for cleaner, more detailed astrophotography results.

The FF90 APO includes a photography extension tube featuring a 2-inch filter thread, making it easy to incorporate filters directly into your imaging setup. Included rear adapters in both M48x0.75 and M54x0.75 thread standards provide broad compatibility with a wide range of cameras, filter wheels, and astrophotography accessories, helping simplify system integration and setup.

The FF90 APO's native flat-field optical design eliminates the need for a separate field flattener, simplifying both setup and operation. With no complicated back focus calculations or spacing adjustments to worry about, astrophotographers can easily connect their camera and accessories, achieve focus, and begin imaging with confidence.

The FF90 APO is equipped with a robust 2.4-inch rack-and-pinion focuser featuring a 10:1 fine-focus reduction, allowing for precise and repeatable focus adjustments critical for astrophotography. A built-in 360° camera rotator makes it easy to frame and orient targets without disturbing focus. For improved portability, the telescope includes a retractable dew shield that reduces its overall length during transport and storage. Precision CNC-machined construction, a durable painted finish, and internal anti-reflection treatments work together to minimize stray light and maximize image contrast. Detachable mounting rings further enhance convenience, making setup and teardown quick and straightforward whether you're imaging from home or traveling to a dark-sky site.