FF90 APO Flat-Field Apochromatic Refractor

The ZWO FF90 is a four-element, fully air-spaced apochromatic optical design refractor with a focal length of 609mm and focal ratio of f/6.8. It delivers a flat focal plane over a 44mm image circle, meaning full-frame sensors will not vignette, and will receive sharp star fields from edge to edge.

Main features

Lightweight & Compact

The ZWO FF90 APO features a 90 mm aperture and 609 mm focal length (f/6.8), offering an excellent balance between portability and performance.

The optical tube weighs just 3.92 kg, with a total system weight of 4.52 kg including mounting rings and dovetail plate.

Four-Element Optical Design

The FF90 APO features a four-element, fully air-spaced apochromatic optical design. All four elements work together to deliver a flat imaging field without the need for an additional field flattener.

One ED (extra-low dispersion) glass element is incorporated to effectively reduce chromatic aberration, resulting in improved color correction and image clarity.

44 mm Image Circle — Full-Frame Support

With a 44 mm image circle, the FF90 APO fully supports full-frame sensors and a wide range of imaging setups.

It delivers sharp star fields with excellent edge-to-edge performance, ensuring consistent image quality across the entire frame.

Native Flat-Field Design

The FF90 APO features a native flat-field optical design, eliminating the need for an additional field flattener.

No complex back focus calculations or spacing adjustments are required—simply attach your imaging setup and start capturing once focus is achieved.

Coarse & fine focus adjustment

Equipped with a rigid 3-inch rack-and-pinion focuser, the FF90 APO offers precise control with a 1:10 coarse & fine focus adjustment mechanism.

A built-in 360° rotator at the rear allows for smooth and accurate camera angle adjustments.

Retractable Dew Shield

The FF90 APO features a retractable dew shield, reducing overall length for improved portability.

Precision CNC machining and a high-quality painted finish, combined with an internal anti-reflection coating, help minimize stray light and enhance image contrast.

Quick-Release Mounting Rings

The mounting rings are detachable, allowing for quick and easy setup or teardown of the telescope.

Photography Extension Tube

The FF90 APO includes a photography extension tube with a 2-inch filter thread, along with rear adapters in M48×0.75 and M54×0.75 standards.

This allows for easy integration with a wide range of imaging accessories.

Optical layout

 

Star field map