A Guide to Selecting a Portable Telescope
If you love appreciating the beauty of stars in a clear sky at night, but live in a city, or even in the suburbs, you may find it challenging to be able to see very much. Even in ideal dark conditions, the human eye can perceive stars of magnitude 6-6.5 (where the higher number indicates an exponentially dimmer star). But in a well-lit city like midtown Manhattan, you may only be able to see stars of magnitude 1.0 with your naked eye. That translates to around six stars at any time of the year! Binoculars or a telescope will help you a lot, even in the city. But, a portable telescope, which you can fold up and take with you to an ideal location, can help you see even deep-sky objects, as dim as magnitude 12!
We’ll study some of the portable telescopes that are available on the market nowadays. Many of them are light and compact enough to fit into a backpack, together with their tripod, so you can carry them along with you. And some have features such as a finderscope and apps to locate objects for you, as well as attachments for astrophotography!
We’ll quickly survey the Best Reviews Guide list of the best portable telescopes. They’re typically easier to master than the larger, more complicated optical instruments. It’s both fun and educational!
What can I accomplish with a portable telescope?
Having a telescope that is compact enough to fit in your backpack is a big convenience. Some of the advantages include:
Better stargazing: If you live in an area with streetlights, it can significantly interfere with how many celestial objects you can see. With a portable telescope, you can take it to remote areas away from light pollution and observe constellations, planets, and other celestial objects in crisp detail.
Better birdwatching: Consider using your portable telescope for daytime observing as well; the sun, moon, and other objects like birds flying overhead can be viewed through specialized solar filters.
Better astrophotography: You could also try astrophotography by attaching your camera to the telescope lens to capture awe-inspiring moments of the cosmos.
Share experiences with others: Portable telescopes are compact and easy to transport, meaning you can share the beauty of the night sky with others by bringing it along on camping trips or sharing a view of Jupiter's red spot with curious neighbors from your own backyard!
What do we mean by a star’s magnitude?
The scale of star magnitudes dates back to the Greek astronomers Hipparchus (190 120 BC) and Ptolemy (100 - 170 AD), who ranked the visible stars on a scale of 1 to 6, with a 1st magnitude star being the brightest, a 6th magnitude star being barely visible. Roughly, a 1st magnitude star is 2.512 times brighter than a 2nd magnitude star, 2.5122 times brighter than a 3rd magnitude star, and 2.5123 times brighter than a 3rd magnitude star, etc.
What is the focal length of a telescope?
The telescope’s focal length is essentially the distance between the objective lens or mirror of the telescope, and the point where the rays from the lens or mirror converge. The focal length is given in millimeters. We’ll see that the objective focal length divided by the eyepiece focal length gives you the telescope’s magnification.
Types of Portable Telescopes
Looking at the Best Reviews Guide’s list of portable telescopes, we can distinguish between refracting telescopes that principally rely on lenses for magnification, reflecting telescopes that rely on mirrors for magnification, and those that use a combination of mirrors and lenses.
Refracting Telescopes: “Refraction” is how light bends when it goes through a medium other than a vacuum, such as air, glass, quartz, etc. A refracting telescope uses lenses for magnification, with a large lens at the far end of the telescope, called the objective lens. The thickness of the lens will determine how much it magnifies. But, the diameter of the lens is also important for stargazing, since you want the telescope to collect as much light as possible. The Celestron 70-mm Portable Refractor Telescope has an objective lens that is 70 mm wide, as well as two eyepieces for low and high power magnification. Despite the objective lens being so wide, the total weight of the telescope is only 4.2 lbs.
Celestron 70-mm Portable Refractor Telescope
Reflecting Telescopes: It’s easier to make a concave mirror that will collect more light and achieve greater magnification than lenses of the same size. A reflecting telescope has a large concave mirror in its base. The wider the mirror, the more light it can collect. For example, the Zhumell Z100 Portable Altazimuth Reflector Telescope has a magnifying mirror (called the “objective mirror”) that is 10 cm in diameter. It comes with two eyepieces, which magnify 24x and 40x, and allow you to magnify objects anywhere from 14x to 200x.
Zhumell Z100 Portable Altazimuth Reflector Telescope
The Zhumell telescope is a Newtonian reflector telescope. Another popular construction of portable reflecting telescopes is the Maksutov-Cassegrain telescope, such as the Sky-Watcher Skymax 102-mm Maksutov-Cassegrain Compound Style Reflector Telescope. It offers less aberration than the traditional Newtonian design, and can achieve the same result as a Newtonian telescope in a telescope tube that is half the length! That certainly adds to the telescope’s portability.
Sky-Watcher Skymax Maksutov-Cassegrain Reflector Telescope
What reviewers say
Here are some customers’ impressions about the portable telescope that they bought:
Not waterproof: Just because these telescopes are portable and intended for you to take with you when camping, don’t assume that they’re also waterproof. There may be spotting scopes with that capability, but these are meant solely for traveling compactly.
Reflector or refractor?: Experts recommend refracting telescopes for beginners, even if they want to dabble in astrophotography since they’re easier to use and master. However, once you gain experience, you may prefer a reflector telescope, since it can achieve higher magnification with the same size aperture as a similar-sized refractor telescope.
Here are some features that are worth looking for when selecting a portable telescope:
Computerized telescopes: Nowadays, even amateur telescopes can be set up and aligned by means of a computer program. The Celestron NexStar 130SLT Telescope comes with a remote control and the SkyAlign program to align the telescope. You aim at three conspicuous objects, and the program locks your telescope in place to find thousands of other objects!
Celestron NexStar 130SLT Telescope
Smartphone app: Some telescopes also allow you to link to your smartphone or tablet computer, to navigate your telescope to the objects you want to view. The Celestron Astro Fi 102 WiFi Reflecting Telescope uses the SkyPortal app for viewing the sky. Others, like the Gskyer 70-mm Refracting Telescope, even include a smartphone mount, so that you can take pictures with your smartphone through the telescope’s eyepiece!
Celestron Astro Fi 102 WiFi Reflecting Telescope
Gskyer 70-mm Refracting Telescope
Magnification: It’s a bit tricky to figure out the magnification of a telescope. It’s not just the magnification of the eyepiece and the magnification of the objective. Rather, it’s given by the telescope’s focal length divided by the focal length of the eyepiece. Thus, it’s important to know your telescope’s focal length, to get a true estimate of what kind of objects you can see in the sky. For example, the Celestron StarSense Explorer LT 80AZ has a focal length of 900 mm, and an eyepiece with a focal length of 10 mm or 25 mm, then the magnification will be 90x or 36x, respectively.
Practical magnification: On the other hand, there’s also the “practical magnification”, or “maximum useful power” of a telescope. It’s given by the diameter of the objective lens in mm times 2. This number tells you how much light the objective lens collects, and how much more powerful it is than the unaided human eye. So, a 70-mm diameter lens or mirror gives you a practical magnification of 140x. The point is, that using a stronger eyepiece to exceed this “maximum useful power” will not achieve anything, since the telescope is limited by how much light it lets in. You may get a set of eyepieces that magnify 24x, 60x, and 120x, but the 120x will not be able to give you any real advantage if there’s not enough light from the object.
Barlow lens: Some telescopes come with a Barlow lens that you can insert in between the eyepiece and the diagonal mirror in a reflecting telescope. It can increase the magnification by another 2x or 3x.
We reviewed some of the specs of the various types of portable telescopes. Since the most important thing is portability, pay attention to the size and weight of the telescope you wish to purchase. Also consider the specs such as focal length, objective diameter, eyepiece magnification, optical coatings, and the like. Once you get started with a portable telescope, you’ll find more and more celestial objects worth viewing!