Frequently asked questions about telescopes

Our comprehensive answers to frequently asked questions about telescopes are designed to help you better understand how they work and how to get the most out of them. If you can't find the answer to your specific question, feel free to contact us – we're always happy to assist!

What are the differences between different types of telescopes?

There are three main types of telescopes: refractors, reflectors, and catadioptrics. Each has the same basic goal of collecting light and focusing it to provide a magnified image for you to observe. However, they achieve this differently:

• Refractors use lenses and are known for delivering sharp, high-contrast images. They are low maintenance but tend to be more expensive as the aperture size increases.
• Reflectors use mirrors and offer larger apertures at lower prices. They’re great for observing deep-sky objects, but require occasional maintenance, like cleaning or realigning the mirrors (collimation).
• Catadioptric telescopes combine lenses and mirrors, offering the benefits of both refractors and reflectors. They’re versatile and portable, but can be pricier and often require more setup time.

For more information on the pros and cons of each type, check out our telescope buyer’s guide.

How far can I see with my telescope?

While telescopes can view objects millions of light-years away, what matters is the brightness of the object rather than distance. Bright celestial objects like the moon, planets, and star clusters can be seen easily, even with smaller telescopes. Distant galaxies, such as the Andromeda Galaxy at 2.5 million light-years, are visible with larger telescopes due to their brightness.

What is the focal length of a telescope?

The focal length is the distance from the telescope’s primary lens or mirror to the point where the image comes into focus, known as the focal point. The longer the focal length, the more powerful the telescope’s magnification, but this also means a narrower field of view. For instance, a 2000mm focal length telescope has double the magnification but half the field of view of a 1000mm focal length telescope. Focal length plays a crucial role in determining both the magnification and the clarity of the image.

Why does my telescope make everything look upside down or mirror-reversed?

It’s completely normal for telescopes, especially refractors and reflectors, to show images upside down or mirror-reversed. This doesn’t impact astronomical viewing because there is no "up" or "down" in space. However, for terrestrial viewing, you can use an image-erecting prism to correct the orientation.

Can I alter the magnification of my telescope?

Yes, the magnification of your telescope is dependent on two factors: the focal length of the telescope and the eyepiece you’re using. To calculate magnification, divide the telescope’s focal length by the focal length of the eyepiece. For example, a 1000mm focal length telescope with a 25mm eyepiece will provide 40x magnification (1000 ÷ 25 = 40). By swapping eyepieces, you can easily increase or decrease magnification, making telescopes highly versatile for different types of viewing, whether it's the moon, planets, or deep-sky objects.

What is a telescope eyepiece, and will my telescope work without one?

A telescope eyepiece is what magnifies the image collected by the telescope’s objective lens or mirror and projects it into your eye. Without an eyepiece, your eye would not be able to see the focused image. However, a telescope can function without an eyepiece if you’re using it for astrophotography or with other instruments, like cameras or spectroscopes.

What’s the best eyepiece and magnification to use on my telescope?

Choosing the right eyepiece depends on your telescope’s aperture and what you’re observing. Each telescope has a maximum useful magnification, typically about 50-60 times the aperture size in inches. Exceeding this limit can result in a blurry or dim image. For general use, lower magnification (6x to 25x per inch of aperture) provides bright, sharp views, especially for wide-field targets like star clusters. Higher magnifications (100x and above) are ideal for detailed lunar, planetary, and binary star observations.

What is a Barlow lens?

A Barlow lens is an accessory that increases the magnification of any eyepiece it’s used with. The most common Barlow lens is 2x, meaning it will double the magnification of your eyepiece. For example, using a 2x Barlow lens with an eyepiece that provides 20x magnification will boost that to 40x. This is a great way to expand the capabilities of your telescope without buying multiple eyepieces. Barlow lenses come in different lengths—short Barlow lenses are typically used with reflector telescopes, while long ones are more suited to refractors.

What is a Telrad or red dot finder, and do I need one?

A Telrad or red dot finder is a popular tool used to help you aim your telescope. It projects a red dot or circle onto the sky, which makes it easier to center celestial objects. Many astronomers prefer using these, especially when paired with a finder scope, as it simplifies the process of aligning your telescope.

What does 'field of view' mean?

Field of view (FOV) refers to the width of the area you can see through your telescope. A wider field of view makes it easier to locate objects in the sky, such as star clusters or nebulae, while a narrower field of view is useful for observing specific objects like planets or the moon in greater detail.

What is the advantage of a large aperture telescope?

Aperture is the diameter of the telescope’s primary lens or mirror, and it is the most important feature to consider. Larger apertures collect more light, making faint objects, like distant galaxies and nebulae, easier to see. Additionally, telescopes with larger apertures have a higher maximum practical magnification, allowing you to see finer details on objects like the moon and planets.

What's the difference between altazimuth (AZ), equatorial (EQ), and Dobsonian mounts?

• Altazimuth (AZ) mounts are simple, manual mounts that move up and down (altitude) and left to right (azimuth). They’re easy to use and great for beginners.
• Equatorial (EQ) mounts are more advanced and designed to follow the arc of celestial objects as the Earth rotates. They require proper alignment with the North Star, but once set up, they make tracking objects much smoother, especially for long viewing sessions or astrophotography.
• Dobsonian mounts are a type of altazimuth mount used on large reflector telescopes. They provide easy movement and stability for bulky telescopes, often favoured for deep-sky observation.

What are the best conditions for stargazing?

The best viewing conditions depend not only on clear skies but also on atmospheric stability, known as seeing conditions. Nights when stars twinkle less tend to provide better viewing. Light pollution, moisture, and the brightness of the moon can also affect what you can see through your telescope.

Do I need a motor drive with my equatorial mount?

A motor drive is a great addition, especially if you plan to use your telescope for astrophotography or long-term viewing. As the Earth rotates, celestial objects move out of your telescope’s field of view, especially at high magnifications. A motor drive will automatically adjust the telescope to keep the object centered, ensuring a smooth viewing experience. It’s particularly useful for observing planets or stars that can drift quickly from view.

What does OTA stand for?

OTA stands for Optical Tube Assembly. This term is used to describe telescopes sold without a mount or tripod. When a telescope is listed as "OTA only," it means you’re buying just the optical tube, so you’ll need to purchase a mount separately.

What is a GoTo telescope and how does it differ from a manual telescope?

A GoTo telescope is motorised and computer-controlled. Once set up, it can automatically locate and track celestial objects at the push of a button, making it easy to observe stars, planets, and deep-sky objects. These are ideal for beginners or those interested in astrophotography. In contrast, manual telescopes require you to manually point and track objects, which can take more time and practice but offers a more hands-on experience.

When’s the best time to observe the moon?

Surprisingly, the best time to observe the moon is not during a full moon. The extreme brightness during a full moon washes out surface details, making craters and mountain ranges harder to see. The best views are typically during the first or third quarter phases when shadows along the terminator (the line between light and dark) create a more detailed, three-dimensional view of the lunar surface.

Why can’t I find the moon, planets, or stars in my telescope?

If you can see an object through your finder scope but can’t locate it through your telescope’s main eyepiece, it’s likely that the two are not aligned. Most finder scopes need to be aligned with the telescope manually. This is best done in daylight by focusing on a distant stationary object, like the top of a building or...a tree, and adjusting the finder scope to match what you see in the telescope’s eyepiece. Be sure never to point your telescope at the sun as this can cause permanent eye damage.

Why is the moon a fuzzy bright light when I look at it?

The most common cause of this issue, especially for first-time telescope users, is that the eyepiece is not focused properly. Focusing a telescope takes time and patience, but once you have it correctly set, it dramatically improves your viewing experience. You’ll be able to see the moon, stars, and planets with the clarity you expect from your telescope.

Here’s how to focus your telescope for a clearer view:

• Remove and reinsert the eyepiece – Start by removing the eyepiece from the eyepiece holder and then securely reinserting it. This ensures that the eyepiece is properly seated.
• Use the lowest magnification eyepiece first – Always begin with the eyepiece that has the highest number written on it (this indicates the lowest magnification). This eyepiece gives you a wider field of view, making it easier to locate objects and adjust the focus.
• Find a large, bright reference point – Aim the telescope at an obvious and easily identifiable reference point, like the moon’s edge. If you are still seeing a fuzzy bright light, gently move the telescope until you can see the edge of the moon or a clear feature, and then begin adjusting the focus.
• Begin focusing – Use the adjustment knobs to gradually bring the image into focus. Start by moving the eyepiece slowly in or out of focus, and you’ll soon get a feel for the correct direction and amount of adjustment needed to make the image sharper.
• Fine-tune the focus – As you get closer to the correct focus, the image should start revealing more details, such as the moon’s craters or the planets' features. Fine-tuning your focus will help you achieve the clearest image possible.
• Practice during the day – If you’re having trouble focusing at night, it can be helpful to practice during daylight hours. Aim your telescope at a distant, recognizable object, such as a tree or building, and follow the same focusing steps. Be extremely careful never to point your telescope near the sun, as this can cause permanent damage to your eyes.

By following these steps, you’ll be able to enjoy much crisper, more detailed views of the night sky and get the most out of your telescope.

If you've got a question that hasn't been answered here then why not check out our telescope buying guide, or send us a message and we'll be happy to help.