A complete guide to buying your first telescope!

So, you've decided to take the plunge and get your first telescope, smart move. But where do you start? With so many options out there, it can feel overwhelming. Fear not! We've got you covered with this complete guide to buying your first telescope. 

Let's dive in and make sure you get the perfect telescope for your cosmic adventures.

A complete guide to buying your first telescope!

Before you hit the store (online or otherwise), take a moment to consider what you really want out of your telescope. Are you interested in visual astronomy, or are you itching to capture stunning astrophotography shots.

A personal choice

Knowing your goals will help narrow down your options and ensure you make the right choice (and avoid wasting money!). Ask yourself:

• What will I use my telescope for? Visual astronomy and astrophotography are two distinct hobbies, each with their own requirements. For example, in visual astronomy the mount is not a crucial aspect, but the telescope aperture makes all the difference in the world. For astrophotography instead, a good, steady mount is essential and it’s where most of the money should be invested. Thus, before buying a telescope, make up your mind and chose what your main goal is.
• What kind of astrophotography am I in? If you decide to be an astrophotographer, the next question you need to ask yourself is what type of photography you want to try. Planetary imaging and DSOs astrophotography have, again, different requirements: for planetary you would have to get the largest scope you can afford and good quality eyepieces whereas for deep sky astrophotography you should invest on a good camera and filters, and the best mount you can afford.
• Where will I use my telescope? Another important aspect to take in consideration is the weight of your gear. If you need to load your car and drive in the middle of nowhere with your telescope, you’ll find that moving a small scope is much easier and sustainable in the long run. If you’re lucky enough to have your own backyard or a terrace instead, you may opt for a larger telescope on a beast mount.
• What’s my budget? This is an obvious one but after you answered these first question you need to decide how much you want to invest before hitting the store. This can be an expensive hobby, and it’s very easy to get carried away so determining the budget in advance will help you get the best combination of mount, telescope and accessories, without breaking the bank.
• Where to buy a telescope? Today’s telescopes are a mix of fine, delicate optics and high-tech electronics so where you buy your telescope is as important as the scope itself. Buying from a professional store will provide you with the best service and invaluable advice from experts in the field whereas getting a telescope off Amazon, for instance, may be cheaper but comes with no support at all.
   

The best telescope is the one you'll actually use!

Everything you need to know about telescopes

To choose the right telescope for your needs, it’s best to familiarise with some of the technical terms you will encounter and that may sound complicated at first; here are the most important ones.

• Aperture.A telescope’s aperture is the diameter of its main optics (lenses or mirrors) measured in millimeters or, for larger apertures, in inches. The aperture determines the telescope’s light-gathering ability (how bright a target appears) and its resolving power (how sharp the target appears). Generally, larger apertures reveal fainter objects and finer details compared to smaller ones.

  However, avoid getting "aperture fever"! Larger apertures make telescopes bigger, heavier, and more expensive. Considering the human eye has an average aperture of 7mm, even the smallest telescope is a significant improvement. Beginner telescopes typically have apertures ranging from 60mm to 300mm (12 inches).

• Focal Length. The focal length of a telescope measures the distance in millimeters from the main optic to the point where the image is formed (either the eyepiece or camera). The focal length determines the scope’s field of view: shorter focal lengths provide a wide field of view, while longer focal lengths offer narrower views. Generally, longer focal lengths are better for planetary imaging and photographing small, faint objects like galaxies and star clusters. In contrast, shorter focal lengths are ideal for capturing larger targets such as nebulas.

• Focal ratio. The focal ratio, a key aspect of astrophotography, measures the "speed" of a telescope's optics. Written as "f/" followed by a number, it's calculated by dividing the scope's focal length by its aperture. For example, a telescope with a 2000mm focal length and a 200mm aperture has a focal ratio of f/10 (2000/200=10).

  All else being equal, a telescope with a lower focal ratio will produce brighter images than one with a higher focal ratio, but it will also have a narrower field of view. This is crucial because slower optics (f/7 and above) require longer exposure times to collect the same amount of light as faster optics.

• Magnification. A telescope’s magnification is its ability to enlarge the observed object, and this concept is straightforward. It is primarily useful for visual astronomy to help determine the best eyepiece to use. Magnification is calculated by dividing the telescope’s focal length by the eyepiece’s focal length. For example, a telescope with a focal length of 2000mm used with an 8mm eyepiece provides a magnification of 250x (2000/8=250).

  As a general guideline, a telescope's maximum useful magnification is about 50 times its aperture in inches or twice its aperture in millimeters. This is an optimistic estimate, as atmospheric conditions and other external factors often reduce this number. Excessive magnification can result in blurry views, so be cautious of telescopes that advertise improbably high magnifications. 

The different types of telescopes

Now, let’s see what our options are in terms of telescopes; there are three main classes, each with their own pros and cons:

• Refractors. Ask any kid to draw a telescope and they will draw a refractor: a long tube with a lens at the front and the eyepiece or camera at the back. Refractors were the first type of optical telescope ever designed and their popularity has remained intact for centuries.

  

  Refracting telescopes are renowned for their ability to produce sharp, high-contrast images using lenses instead of mirrors. This design makes them particularly well-suited for wide field astrophotography. However, their typically shorter focal lengths mean they are less effective at resolving fine details on distant galaxies, globular clusters, or planets.

  Despite this limitation, refractors remain popular among beginners as they require virtually no maintenance and are more forgiving when it comes to mount tracking imperfections. Their compact and lightweight design also makes them ideal for astronomers who prefer portable setups or frequent outdoor observation sessions.

  Consider investing in an apochromatic (APO) refractor, which uses lenses made from extra-low dispersion (ED) glass to minimize chromatic aberration found in achromatic refractors. Also, most refractors require a field flattener to correct optical distortions and enhance edge sharpness.

• Reflectors. Reflector (or Newtonian) telescopes offer the larger aperture for the money! This is because they employ mirrors, which are generally more cost-effective to manufacture than lenses.

  

  Reflectors mount a large primary mirror at the bottom of the telescope tube to gather light; this reflects the light to a secondary mirror, which then directs it to the side of the tube where it meets the eyepiece or camera. While cheaper, this system requires continuous adjustments to ensure that the mirrors be perfectly aligned; this practice is called “collimation” and is often regarded as the main disadvantage of such optics.
  
  At mid-size aperture, reflectors usually work best with focal ratios between f/4 and f/8, useful for wide field astrophotography. With large apertures, instead, reflectors are generally optimized for visual observations of faint, deep-sky objects such as nebulae and galaxies, but require much sturdier mounts for astrophotography.

• Catadioptric. Catadioptric telescopes blend the desirable features of both refractors and reflectors by employing a combination of lenses and mirrors. The two most popular types among amateur astronomers are the Schmidt-Cassegrain and Maksutov-Cassegrain telescopes.

  

  These designs incorporate a corrector plate at the front and a curved mirror at the back, similar to a refractor but with the eyepiece positioned at the rear. The hallmark of catadioptric telescopes is their compact and lightweight construction, making them more portable than refractors or reflectors of similar aperture size.
  
  They typically boast long focal lengths and slow focal ratios (> f/10), which are advantageous for observing small celestial targets such as planets, galaxies, and star clusters. Some models also offer the option to use focal reducers to shorten the focal length and widen the field of view, albeit at an additional cost.
  
  Despite their benefits, catadioptric telescopes have drawbacks to consider. Like reflectors, they require precise collimation to ensure optimal performance. Additionally, their compact design makes them prone to dew formation on the corrector plate, necessitating the use of extension tubes and electric dew heaters, which add to the overall expense. Furthermore, these telescopes take longer to reach thermal equilibrium with the nighttime temperature, a critical factor for achieving clear, high-quality images. As a result, astronomers often need to set up catadioptric telescopes outdoors well in advance of their observation sessions to allow sufficient time for cooling. 

The different types of mounts

Now, let's discuss one of the most crucial elements in astronomy: the mount. For anyone serious about astrophotography, investing in a stable and precise mount is paramount. Even the highest-quality telescope will underperform without a reliable mount.

Many telescopes, particularly those aimed at beginners, come bundled with a mount and tripod as a convenient package. While this may seem like a simple and cost-effective choice, it's generally advisable to forgo these packages if your intention is astrophotography. Instead, investing in a dedicated and robust mount from the outset will save you both time and money in the long run.

• Alt-azimuth mount. An "Alt-Az" mount, short for Altitude-Azimuth, operates with two axes to track celestial objects: one for altitude (up/down) and the other for azimuth (left/right along the horizon). 

  This simplicity makes Alt-Az mounts popular among beginners due to their ease of setup, relatively light weight, and portability. They are also generally more affordable compared to other mount designs.

  Among Alt-Az mounts, Dobsonian mounts are particularly well-known. These mounts replace the traditional tripod with a simple wooden platform directly on the ground, allowing for a 360° rotation. Dobsonian mounts are prized for their affordability and capability to support very large Newtonian telescopes.

  However, Alt-Az mounts have limitations for deep sky astrophotography. They do not compensate for the Earth's rotation, restricting exposure times to 20-30 seconds before "field rotation" becomes noticeable. This rotation causes stars to appear elongated, creating star trails in images.

  While planetary imaging and visual astronomy are well-suited to Alt-Az mounts, equatorial mounts are preferred for achieving superior results in deep sky object astrophotography.

• Equatorial mount. If deep sky astrophotography is your primary goal, investing in a sturdy and precise equatorial (EQ) mount is essential. Unlike Alt-Az mounts, EQ mounts operate on two axes: right ascension (east/west) and declination (north/south). The key feature of an EQ mount is its ability to align one axis, right ascension, parallel to Earth's rotational axis through a process called "Polar alignment".  

  This alignment allows the EQ mount to compensate for the Earth's rotation, effectively eliminating field rotation during long exposures. This capability is critical for capturing faint details of deep sky objects.

  EQ mounts are rated for maximum payload, indicating the maximum weight they can support while accurately tracking celestial objects. For astrophotography, it's recommended to use no more than 60-70% of the maximum payload to ensure stable tracking. For example, a mount with a 30 kg (66 lbs) maximum payload should ideally handle 18-21 kg (40-46 lbs), accounting for the weight of the telescope, camera, guiding system, and accessories.

  However, EQ mounts are larger and significantly heavier than Alt-Az mounts, which limits their portability—something to consider if you need to transport your telescope frequently at night. Moreover, EQ mounts are generally more expensive than comparable Alt-Az mounts, requiring a significant financial investment. These factors highlight the importance of choosing the right mount based on your specific needs and budget when pursuing deep sky astrophotography.

Expectations vs. reality

Now that you know the major components and features of a telescope and are ready to become an amateur astronomer or astrophotographer, there's one last crucial point: lower your expectations! Observing the Moon, the Sun (with the appropriate solar filter!), or the planets through a telescope is breathtaking.

However, our eyes aren't as sensitive to light as cameras, so the views will never match captured images. Seeing Saturn's rings or Jupiter and its moons is unforgettable, but they will appear as yellowish bodies without the vivid colors seen in photos.

Observing objects outside our Solar System can be disappointing without knowing what to expect. Due to their distance and light pollution, deep sky objects like nebulas or galaxies will appear as fuzzy, featureless blobs, even with powerful telescopes. The human eye can't capture faint details or colors.

However, double stars and star clusters can offer beautiful views with the right telescope. Filters can also enhance the contrast and color of nebulas and galaxies. Always keep in mind this: you're peering at objects thousands or millions of light years away!