What a refracting telescope does
A refracting telescope uses a lens at the front, called the objective, to bend light to a focus. An eyepiece magnifies that focused image. The design is the classic “spyglass” layout, and it was the first kind of telescope used for astronomy. Galileo is widely credited as one of the first to turn a telescope on the sky in 1609, and he used a refractor-type design, though he was not the inventor of the telescope itself.
Today refractors remain popular for several practical uses.
Viewing the Moon and planets
Refractors are often chosen for lunar and planetary observing. Their unobstructed light path and sealed tubes can deliver crisp, high-contrast views. With a decent refractor you can expect to see lunar craters and mountains, Jupiter’s cloud bands and its four bright moons, Saturn’s rings, and the phases of Venus.
Double stars and bright star clusters
Splitting close double stars is a good test of optics and seeing, and refractors are well suited to it. Brighter, larger star clusters also look good, especially in short refractors that offer wide fields of view.
Wide-field deep-sky viewing and astrophotography
Short-focal-length refractors, often called “widefield” or “rich-field” scopes, give sweeping views of the Milky Way, large star clusters and extended nebulae. Apochromatic refractors are popular for astrophotography because they combine low false color with flat, sharp images when paired with a field flattener. A tracking mount is essential for long exposures.
Faint galaxies and nebulae are limited by aperture, though, and refractors in common price ranges are small. For those targets, a reflector often offers more. See refractor vs reflector telescopes for the comparison.
Terrestrial and daytime use
Refractors can also be used on land, such as for birdwatching, nature viewing and landscapes. A correct-image diagonal or a dedicated spotting scope flips the view upright. Astronomical telescopes, by default, often show an inverted or mirrored image, which is fine for the sky but awkward on land. For more on this, see spotting scope vs telescope.
Education and outreach
Their durability and low maintenance make refractors common in schools, public observatories and outreach events. They are also good for first-time observers because there is little to adjust.
Professional history
Large refractors were important in 19th-century astronomy, when many important double-star and planetary observations were made. As lenses are heavy and can only be supported around the edge, modern research telescopes use mirrors instead.
Disadvantages of refractors
- Cost per inch of aperture rises sharply with size.
- Chromatic aberration is visible in many achromatic models as colored fringes on bright objects. Apochromatic designs reduce it at higher cost.
- Long tubes on larger models can be unwieldy and need a sturdy mount.
- Limited aperture compared with reflectors at similar prices, so faint deep-sky objects look dimmer.
Achromats vs apochromats
An achromat uses a simple two-element lens and is the budget option. An apochromat (APO) uses special glass or extra elements and brings colors together more closely. For visual use of the Moon and planets, many beginners are happy with a good achromat, particularly one with a longer focal ratio, which tends to show less color fringing.
Is a refractor right for you?
A refractor is a good choice if you want low maintenance, quick setup and sharp views of the Moon and planets, or a portable wide-field scope. If your priority is faint deep-sky objects, consider a reflector or a compound design. See telescope types explained for an overview of all the main designs.