90 mm four-element apochromatic telescope, 609 mm focal length, with a naturally flat field of view for astrophotography.
CHF 773.10incl. Swiss VAT
Part Number ZWO-A195516
90 mm four-element apochromatic telescope, 609 mm focal length, with a naturally flat field of view for astrophotography.
The corrector is part of the optical design: an additional flattener is not required in the native configuration provided by ZWO. The 44-mm image circle is specifically designed for full-frame sensors. The choice of camera depends on the focal length, pixel size, and intended targets. The retractable dew shield facilitates transport; the detachable clamps allow for mounting on a compatible dovetail. The eyepiece holder features a geared focus mechanism and rear rotation to adjust the framing. Adjust the focus using the actual photography setup, including filters. Ensure compliance with the mount’s mechanical range and check cable routing throughout the mount’s full range of motion. This product corresponds to the FF90 APO optical tube; kits with a mount are sold separately.
Documentation and Compatibility: ZWO official data sheet.
The ZWO FF90 APO is a flat-field ED quadruplet refractor with a 90 mm aperture and a focal length of 609 mm (f/6.8), designed primarily for deep-sky astrophotography. Its focal length is ideal for medium-sized nebulae (Orion, the Lagoon, the Trifid, and the Rosette), large galaxies such as M33 or the M81-M82 pair, and star clusters. At f/6.8, its standard aperture ratio requires slightly longer exposure times, but in return delivers very fine star details.
With an APS-C camera featuring 3.76 µm pixels (Sony IMX571 sensor), you get approximately 1.27″ per pixel for a field of view of 2.2° × 1.5°. With the 0.75× crop factor, this increases to 1.7″ per pixel and a field of view of 2.9° × 2°. The 44 mm image circle covers full-frame sensors (24 × 36 mm), so a full-frame mirrorless camera will also work.
No. Its optical design (flat-field ED quadruplet) inherently produces a flat field, with sharp stars all the way to the corners, without the need for an external field flattener. To increase the field of view and brightness, the dedicated reducer (Askar 91F 0.75× Reducer) the aperture to 457 mm at f/5.1.
45 to 75 mm. This distance is measured from the thread to the sensor, including the rings, filter wheel, and filter drawer: adhering to this measurement down to the millimeter ensures that the stars remain round in the corners.
The tube weighs about 3.9 kg; with the camera, filter wheel, and guide scope, expect it to weigh around 5.4 kg: an HEQ5-R Pro-class mount provides plenty of headroom. A refractor requires no collimation: once balanced, it’s ready to use as soon as it reaches operating temperature.
Yes, as a bonus: with an angled mirror and an eyepiece, it provides high-contrast images without false colors of the Moon, the planets, and double stars.
