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.
Showing 81–94 of 94 resultsSorted by popularity
Showing 81–94 of 94 resultsSorted by popularity
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.