Choosing a Telescope

Telescope Types

Refractors use a glass lens at the front of the tube to bend and focus light. They produce sharp, high-contrast images and require virtually no maintenance because the optics are sealed inside the tube. Refractors are excellent for observing the Moon, planets, and double stars, where contrast and resolution matter most. Their main disadvantage is cost: quality refractors with apertures above 100mm become expensive because the glass lens must be precisely figured on all surfaces. For beginners, a 70mm to 90mm refractor on a sturdy mount is a solid choice for planetary viewing and casual stargazing.

Reflectors use a curved mirror at the bottom of the tube to collect and focus light. The most popular design for amateur astronomers is the Newtonian reflector, which uses a flat secondary mirror to redirect the light to an eyepiece on the side of the tube. Reflectors offer much more aperture per dollar than refractors because mirrors are cheaper to manufacture than lenses. A 150mm (6-inch) Newtonian reflector costs about the same as a 70mm refractor but gathers over four times as much light. The Dobsonian mount, a simple alt-azimuth base for large Newtonian reflectors, provides the best value for deep-sky visual observing.

Compound (catadioptric) telescopes combine lenses and mirrors to fold the optical path into a compact tube. The two most common designs are the Schmidt-Cassegrain (SCT) and Maksutov-Cassegrain. These telescopes are highly portable for their aperture, work well with computerized tracking mounts, and are versatile for both visual observing and astrophotography. Their main disadvantage is higher cost per inch of aperture compared to simple Newtonians, and they typically require more time to reach thermal equilibrium with the surrounding air.

Understanding Aperture and Magnification

Aperture is the single most important telescope specification. A telescope with a larger aperture collects more light, allowing you to see fainter objects, and provides higher resolution, allowing you to see finer details. Doubling the aperture quadruples the light-gathering power and doubles the theoretical resolution. A 200mm telescope can reveal thousands of deep-sky objects (galaxies, nebulae, star clusters) that are invisible through a 70mm telescope.

Magnification is determined by dividing the telescope's focal length by the eyepiece focal length. A telescope with a 1000mm focal length using a 25mm eyepiece produces 40x magnification. While it might seem that higher magnification is always better, the maximum useful magnification is limited by the aperture: roughly 2x per millimeter of aperture (so about 300x for a 150mm telescope). Beyond this, the image becomes dim, blurry, and shaky. For most observing, low to moderate magnification (50x to 150x) provides the best views because it maximizes brightness and field of view.

Eyepieces are interchangeable, so a single telescope can provide a range of magnifications. A good starter set includes a low-power eyepiece (around 25mm) for wide-field views of star clusters and nebulae, a medium-power eyepiece (around 10mm) for detailed views of the Moon and planets, and a high-power eyepiece (around 6mm) for splitting close double stars and observing planetary detail on the best nights. Plossl eyepieces offer good performance at moderate cost, while more expensive designs like Televue Naglers provide wider apparent fields of view and better edge sharpness.

Mounts and Tracking

The mount is at least as important as the telescope itself. A shaky or inadequate mount will make observing frustrating regardless of the optical quality. Alt-azimuth mounts move up-down and left-right, making them intuitive and easy to use. The Dobsonian mount, which is simply a large alt-azimuth base for Newtonian reflectors, is the most popular choice for visual deep-sky observing because it is stable, inexpensive, and allows smooth manual tracking.

Equatorial mounts are aligned with Earth's rotational axis, allowing objects to be tracked across the sky by turning a single axis. Motorized equatorial mounts can track automatically, keeping objects centered in the eyepiece without manual adjustment. These mounts are essential for astrophotography, which requires long exposures during which the telescope must track the sky precisely. German equatorial mounts and fork mounts are the two most common equatorial designs.

Computerized GoTo mounts can automatically find and track thousands of objects from a built-in database. After a brief alignment procedure using two or three known stars, the mount can slew to any object in its catalog at the press of a button. While GoTo mounts are convenient, they add cost and complexity, require power (usually from batteries or a portable power supply), and can discourage learning the sky. Many experienced amateur astronomers prefer manual star-hopping with a non-motorized Dobsonian, using a star chart or app to navigate from familiar stars to unfamiliar targets.

Practical Recommendations

For visual observing of the Moon, planets, and bright deep-sky objects on a modest budget, an 8-inch (200mm) Dobsonian reflector offers extraordinary value. It provides enough aperture to reveal Saturn's rings, Jupiter's cloud bands and moons, hundreds of star clusters, dozens of nebulae, and many galaxies, all for a price comparable to a mid-range refractor with less than half the aperture. The main trade-off is size and weight: an 8-inch Dobsonian is bulky and works best when you have storage space and a nearby observing site.

For portability, a quality 80mm to 100mm refractor on a lightweight tripod or a 5-inch Maksutov-Cassegrain fits easily in a car and can be set up in minutes. These smaller telescopes excel at planetary viewing and are suitable for observing from a balcony or taking on trips. They will not show as many deep-sky objects as a larger Dobsonian, but they provide crisp, high-contrast views of the Moon and planets.

For astrophotography, a sturdy equatorial mount with accurate tracking is more important than the telescope itself. Many astrophotographers start with a camera lens on a tracking mount before adding a telescope. A quality equatorial mount (such as the Sky-Watcher HEQ5 or iOptron CEM26) paired with a small refractor or Newtonian astrograph provides an excellent platform for capturing images of galaxies, nebulae, and star clusters.