ZWO FF90 APO 90mm f/6.8 Quadruplet Refractor

More reach than a 70mm, still light enough to travel

The ZWO FF90 APO is a 90mm f/6.8 quadruplet apochromatic refractor with a built-in field flattener and a full-frame 44mm image circle. It hits the sweet spot between portability and aperture: about 65% more light than a 70mm scope and a longer 609mm focal length, at just 3.92kg (8.6lb). If it looks familiar, that's because it's ZWO's version of the Askar 91 F-Series.

Key specs: 90mm aperture · 609mm f/6.8 · 44mm full-frame image circle · built-in field flattener · 3.92kg (8.6lb) tube · 3" dual-speed rack-and-pinion focuser

Questions about building a setup around it? Our team is happy to help.

What you can image and see

• Nebulae: the Eagle, Lagoon and Trifid nebulae, the Rosette, and the Crescent Nebula with room around it.
• Galaxies: the Andromeda Galaxy, Bode's and Cigar galaxies in one frame, and the Pinwheel Galaxy.
• Star clusters: the Pleiades with its reflection nebulosity and the Double Cluster.
• Visual: sharp, color-free views of the Moon, planets at moderate power and bright deep-sky objects.

No flattener, no spacing math

Most refractors need a separate field flattener set at an exact distance from the sensor. The FF90 APO's four-element, air-spaced design (with one ED element) has the flattener built in, so there's no back focus to calculate: as long as your camera and adapters add no more than 75mm behind the M48 thread, you'll reach focus with sharp stars to the corners. The included photography extension tube and M48/M54 adapters connect dedicated astronomy cameras, DSLRs and mirrorless cameras, and the 360° rotator lets you frame your target without touching focus.

What to add for the best results

• A mount (required): the ZWO AM3N is a great match. Or save time with the ZWO 90APO + AM3N bundle.
• A camera: the ZWO ASI2600MC Pro (APS-C, cooled) is a popular pairing; the ZWO ASI533MC Pro is a great-value cooled color camera with a square sensor.
• Guiding: the ZWO 30F5 Mini Guide Scope with an ASI120MM Mini guide camera mounts right on the handle.
• Control and focus: the ASIAIR PLUS runs the whole rig from your phone, and the ZWO EAFN electronic focuser keeps stars sharp as the temperature drops.
• Filters: for city and suburban skies, a ZWO Duo-Band filter in a ZWO M54 2" filter drawer cuts light pollution on nebulae.
• For visual use: a 2" star diagonal like the Celestron 2" Dielectric Star Diagonal plus your eyepieces.

FF90 APO vs. the other ZWO FF refractors

Still deciding? Browse all our refractor telescopes or the full ZWO telescope lineup.

What's in the box

• FF90 APO optical tube with handle, tube rings and dovetail plate
• Photography extension tube with M48 and M54 adapters

Mount, camera, diagonal and eyepieces are sold separately.

ZWO FF90 APO FAQ

Do I need a field flattener with the FF90 APO?

No. The flattener is built into the optics, so stars stay sharp to the corners of a full-frame sensor, and there's no exact back focus to hit: as long as your camera and adapters add no more than 75mm behind the M48 thread, you'll reach focus.

Which camera works best with the FF90 APO?

An APS-C sensor like the ASI2600MC Pro gives about a 2.2° × 1.5° field at 609mm, great for mid-size nebulae and galaxy groups. The 44mm image circle also covers full-frame sensors. DSLR and mirrorless cameras also work with the matching T-ring.

What mount do I need for the FF90 APO?

At 4.52kg (10lb) with rings and dovetail, the FF90 APO pairs well with the ZWO AM3N once you add a camera, guide scope and ASIAIR. If you plan to add heavier gear later, the ZWO AM5N gives you more headroom. See the ZWO 90APO + AM3N bundle for a matched setup.

Can I use the FF90 APO for visual observing?

Yes. The focuser accepts 1.25" and 2" accessories, so add a star diagonal and eyepieces. The color-free optics give crisp views of the Moon, planets and star clusters.

FF90 or FF110?

The FF110 gathers about 50% more light and its 766mm focal length suits smaller galaxies, but it weighs half again as much and needs a bigger mount like the AM5N. The FF90 keeps the whole setup light and portable on an AM3N.

Specifications