Telescopes

With thousands of options out there, deciding which is the best telescope for you can be overwhelming. Our blog Choosing the Best Telescope for Beginners is perfect for a few quick recommendations, or continue reading below to learn more about telescopes.

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Different Types of Telescopes for Sale

Choosing the right telescope for your needs and budget doesn't have to be hard. Read about the pros & cons of each main telescope type below to help you make an educated buying decision.

Refractor Telescopes

An optical diagram showing the light path entering a refractor telescope. Light enters through the front, passes through glass lenses, and exits out the rear into an eyepiece or camera.Diagram credit: Celestron

Refractors are what most people picture when they imagine a telescope. Using glass lenses, refracting telescopes gather incoming light down a long, narrow tube. Refractors are great for those on a budget as they are the least expensive type of beginner telescope. They also require the least amount of maintenance, which is a huge plus.

However, most entry-level doublet refractors won’t provide as good of a view as a similarly-priced reflector or catadioptric because of their smaller aperture. On the other hand, higher-end triplet refractors can provide some of the best views and images of any telescope type and are an excellent choice for astrophotography imagers of all skill levels.

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Reflector Telescopes

An optical diagram showing the light path entering a reflector telescope. Light enters through the front, passes down to the back, reflects off the primary mirror, reflects off the secondary mirror, and exits out the side into an eyepiece or camera.Diagram credit: Celestron

Reflector telescopes use mirrors to gather incoming light. For the same price as a refractor, you can get a much larger aperture reflector. This larger sized telescope comes at a cost, however, since a larger telescope is heavier and more difficult to transport. 

Almost all reflectors need frequent alignment of the mirrors, which is known as collimation. You can think of collimation as tuning an instrument before playing — it only takes a few minutes, but you’ll need to buy a collimator to keep your telescope “in tune.”

One of the most common subtypes of reflectors is the Dobsonian, which is widely considered to be one of the best types of telescopes for visual observing. Other reflectors include the Newtonian, which you can read more about below, and the Ritchey Chretien, which is primarily used for deep sky astrophotography.

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Catadioptric Telescopes

An optical diagram showing the light path entering a catadioptric telescope. Light enters through the front, passes down to the back, reflects off the primary mirror, bounces up to the secondary mirror, and reflects out the back again into an eyepiece or camera.Diagram credit: Celestron

Catadioptric telescopes, also sometimes called compound telescopes, combine both lenses and mirrors. By using both, these telescopes can offer high quality optical performance in a relatively affordable package. They also yield very high magnification views in a small telescope, thanks to what’s known as a folded optics design. Though usually more expensive, entry-level catadioptrics typically come pre-packaged with an automated mount that takes the headache out of manually finding objects in the night sky. 

By far the most popular subtype of catadioptric telescopes is the Schmidt Cassegrain Telescope, or SCT for short. These versatile scopes offer a jack of all trades assortment of features but come with a higher price tag. Another subtype is the Maksutov Cassegrain, or Mak Cass, which are also great performers with a bit less versatility for a lower price than SCTs.

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Schmidt Cassegrain Telescopes (SCT)

An image of a Schmidt Cassegrain Telescope (SCT) mounted onto a computerized fork mount.

We can’t bring up SCTs without mentioning major telescope manufacturers Celestron and Meade, who pioneered affordable telescopes with quality optics in the form of the Schmidt Cassegrain Telescope (SCT).

The SCT offers very high magnification views in a smaller package than a Dobsonian, making it great for visual observing of the Moon and planets. SCTs are the preferred telescope for many of the world’s best planetary astrophotography imagers. Higher-end SCTs can also be excellent deep sky imaging telescopes too, making the SCT a tough telescope to beat if you’re looking for all-around versatility.

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Dobsonian Telescopes

An image of a large Dobsonian Telescope, which includes a Newtonian telescope mounted onto a swivel-style Dobsonian base.

The Dobsonian telescope is a subtype of reflector telescopes, and is essentially a Newtonian that comes with a swivel-style mount for easy aiming. The Dobsonian is our favorite telescope for visual observing since it gives you the best bang for the buck for aperture. Larger Dobsonians tend to be cumbersome and heavy, making them difficult to bring outside and transport. 

While Dobsonians (or Dobs for short) are good for simple through-the-eyepiece smartphone imaging, their built-in mount is not designed to do deep sky astrophotography. If you’re just doing visual observing, however, a Dobsonian is hard to beat at any skill level. Many of the most dedicated visual amateur astronomers swear by their large Dobs.

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Newtonian Telescopes

An image of a Newtonian telescope, which is a long, thick tube with the secondary mirror showing in the front.

The Newtonian telescope is one of the oldest telescope designs and was designed by Sir Isaac Newton himself, hence the name. Newtonians are good telescopes for both visual observing and astrophotography, but typically you will need added accessories at an extra cost to make the most of them, such as a coma corrector for imaging. 

They also need to be collimated frequently, which tends to steer some users away from them in favor of refractors or SCTs. If you can handle some light maintenance, though, a Newtonian is a great way to get a lot of aperture at a low cost.

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Solar Telescopes

An image of a solar telescope, which features a red glass lens element at the front which is a hydrogen alpha filter to greatly cut down incoming sunlight.

Solar telescopes, designed for observing the Sun, come in many forms. Most solar telescopes are repurposed refractors with special hydrogen alpha filters in them designed to cut down the Sun’s overwhelmingly powerful light for safe observing. Although most telescopes can use a white light filter to safely observe the Sun, a dedicated solar telescope with hydrogen alpha filters can provide a next-level experience with unmatched detail on the Sun’s surface.

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Telescope FAQs

Which telescope can see planets?

Long focal length catadioptric telescopes like Schmidt-Cassegrains and Maksutov-Cassegrains often provide the best views of planets, which appear very small in the sky. However, you can typically see Jupiter's four main moons and Saturn's rings with almost any telescope, including beginner-level refractors.

What should I look for in a telescope?

While everyone's goals are different, we recommend the largest aperture telescope you can both carry and afford. A 6" Dobsonian telescope will provide fantastic views for the price. If you have specific goals in mind, we strongly recommend reading our guide called Choosing the Best Telescope for Beginners.

What is a telescope used for?

A telescope is used to view distant objects. The larger the telescope, the more light it gathers and the more detailed the view will be. Telescopes can be used to observe objects like planets, the Moon, galaxies, nebulae, the Sun, and even ground-based objects like birds and wildlife.

How does a telescope work?

Telescopes work by using glass lenses and/or mirrors to gather and magnify the light from distant objects, which allows us to see faraway objects in much more detail than we can with the naked eye.

There are three main types of telescopes:

Each type has its pros and cons. To compare each type, we recommend reading our blog Choosing the Best Telescope for Beginners. There, you’ll find a chart with the best uses for each type of telescope to help you make a more informed buying decision.

Who invented the telescope?

A Dutch eyeglass maker named Hans Lipperhey (also known as Hans Lippershey) is generally accepted as the inventor of the telescope, as he was the first to file a patent for it in 1608. However, it is not known if Lipperhey actually built the first telescope, or whether he was simply the first to file a patent for it.

When was the telescope invented?

Hans Lipperhey filed the first patent for the telescope in 1608. Just over a year later, in early 1610, Galileo Galilei recorded the first observations of the four largest moons of Jupiter orbiting the planet using his own improved telescope design. This proved for the first time that not everything orbited the Earth, which was a widely accepted theory at that time. The telescope quickly became a powerful scientific tool, and changed our understanding of the universe.

How to use a telescope

Each telescope is a little different, but generally speaking, you can use a telescope by first aiming it at a distant object, then looking through the eyepiece and adjusting the telescope's focusing knob to bring the object into focus. Do not ever point the telescope at the Sun without a proper solar filter, as you can go blind. If you need more specific instructions, consult the manual that came with your telescope.

Where to buy a telescope

We offer hundreds of different telescopes here at Agena Astro, and every single one ships 100% free to the lower 48 United States, unlike most of our competitors. We also offer a 30-day return policy if you decide for any reason you are not satisfied.

 


Defining Telescope Terms

What is aperture?

Aperture measures the diameter of the largest glass element of a telescope. The larger the aperture, the better the view you will get thanks to more light gathering ability. Aperture is usually written out in inches or millimeters, e.g. an 8” or 200mm aperture telescope.

 

What is focal length?

Focal Length is the length (in millimeters) between a telescope's primary lens/mirror and the plane where light comes to focus, which you’ll see written out as 600mm. A telescope with a longer focal length will give a more magnified view, but at the cost of being dimmer.

 

What is focal ratio?

Focal Ratio is simply a telescope's focal length divided by the aperture, which you'll see written out as f/8. The lower the focal ratio number, the brighter the view, but this usually comes at the cost of less detail on objects like planets and the Moon. Conversely, the higher the focal ratio, the fainter the view, but more detail can usually be seen. 

You’ll often read that a lower focal ratio number like f/4 is a “fast” telescope, whereas a high focal ratio like f/10 is a “slow” telescope. Generally speaking, a focal ratio of around f/10 or more is best for viewing the planets and the Moon, whereas a focal ratio around f/4 is ideal (but not required) for viewing deep sky objects like galaxies and nebulae.

 

What is telescope magnification?

Magnification is how many times an object appears magnified through a telescope & eyepiece compared to the naked eye, which you’ll see written as 200x. To calculate this, take the focal length of your telescope divided by the focal length of your eyepiece. A telescope with a focal length of 1000mm paired with an eyepiece with a focal length of 20mm will yield a magnification of 50x. The higher the number, the more “zoomed in” the view will appear, but telescopes and eyepieces have their limits:

 

What is maximum useful magnification?

Maximum Useful Magnification is the most magnification you can get with a given telescope & eyepiece when sky conditions are nearly perfect. To calculate this number, multiply the aperture in inches by 50, or the aperture in millimeters by 2. For example, a telescope with a 6” (150mm) aperture has a maximum useful magnification of 180x.

This is yet another reason why aperture is the most important specification, as the larger the aperture, the more magnification you can push a telescope to, and therefore the more detail you can see. This is especially important for viewing objects like planets, which are extremely small in most telescopes.

 

What is an Optical Tube Assembly?

An Optical Tube Assembly, or OTA for short, is a fancy name for a telescope without the mount. Most of the time you see this term, it means that a telescope is being sold without a mount or tripod to go with it. 

Beginner telescopes will almost always come with a telescope & mount together. Higher end telescopes will usually only come as the OTA only. This is also true where users prefer more customization like in astrophotography, and most imagers opt for an equatorial mount.