Refractor OTA (Optical Tube Assembly)

Are you ready to reach the absolute pinnacle in astrophotography or visual observations? Then the choice of a separate refractor OTA (or, Optical Tube Assembly) The ultimate step. By purchasing a separate tube, you have complete freedom to combine it with a (GoTo) mount you already own. In this category, you’ll find high-quality apochromatic refractors (APOs) from top-tier brands such as Sky-Watcher and TeleVue. Thanks to their advanced ED triplet or quadruplet designs, these tubes completely eliminate color fringing (chromatic aberration). The result? Razor-sharp, high-contrast images and pin-sharp stars from corner to corner on your camera sensor.

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Refractor OTA: the tube that you put on your own mount

A refractor OTA (Optical Tube Assembly) is the standalone lens telescope without mount and tripod. This is the largest subcategory within refractors, and that is no coincidence: astrophotographers choose their mount and their tube separately. From a 40 mm Askar for a star tracker to a 156 mm William Optics Fluorostar for a fixed observatory. Almost everything here is ED or APO; the occasional achromats (Startravel, Evostar) are intended for visual use or as a wide-field finder.

Choose based on the brand point distance, not on the opening

180 to 300 mm. Wide-angle: Milky Way, Andromeda, North America Nebula. On a star tracker or small EQ. Askar FMA180 Pro, William Optics RedCat 51.
350 to 450 mm. The most used class. Flat field of view with flattener, fits on an EQ5 or HEQ5. William Optics ZenithStar 61, Sky-Watcher Evolux-62ED, Sky-Watcher Evostar 72ED, ZWO FF65 APO.
500 to 700 mm. Smaller nebulae and the bright galaxies. Sky-Watcher Evolux-82ED, William Optics GranTurismo 81, Omegon Pro 85/510 Triplet, Askar 103 APO.
800 mm and more. Galaxies and planetary nebulae, and visually the sharpest planetary images. Sky-Watcher Evostar 150ED, William Optics Fluorostar 132, TeleVue NP-101is.

Doublet, triplet of Petzval?

An ED doublet (Evolux, Evostar ED, ZenithStar) is lightweight and affordable and requires a separate flattener. A triplet (GranTurismo, Omegon Pro, Askar) corrects color better and is the standard for serious astrophotography. A Petzval or quintuplet (RedCat, ZWO FF65, Omegon Pro Quintuplet) has the field flattener built-in: no extra optics, no spacing issues, sharp right out to the corners immediately.

What you need for it

A mount with at least twice the payload capacity of the tube plus camera, a flattener or reducer for doublets and triplets, and a finder scope or guidescope for autoguiding. Complete sets with mounts can be found at GoTo refractors; the assemblies themselves included accessories. Brand pages: William Optics, Sky-Watcher, Omegon, ZWO.