We spent more than 20 hours scouring the internet for every written resource on buying your first telescope. We went to the Rose City Astronomers Telescope Lab in 2017, and we interviewed its members and the club president about the most common trials and tribulations they’ve witnessed as the new sky watchers start looking up. While in LA we stopped by the well known Woodland Hills camera and telescope, as well as the Griffith Observatory talk to the staff.
After interviewing our experts and reading NightWatch: A Practical Guide to Viewing the Universe, Terence Dickinson’s reference par excellence, as well as receiving advice from sources published on GeekWrapped, Space.com, Sky & Telescope, and the inner tract of Cloudy nights forum, we had a pretty clear idea of what we were looking for.
Opening it may be the most talked about component of a telescope. Aperture is the diameter of the telescope’s mirror or lens and determines the amount of light the telescope lets in and, in turn, the sharpness of the image.
It can be said that these criteria correspond to the strength and power of the telescope. Yet, as Mounsey of Woodland Hills Camera & Telescopes and Oak Canyon Astronomy Group warned us, one mistake beginners make when choosing a telescope is to think that bigger is always better when it comes to aperture. A larger aperture often means a higher price and a bulkier telescope.
As Mounsey pointed out, the need for greater openness depends on where you are looking and what you hope to see. If you are viewing super-dark skies with the hope of seeing deep-sky objects such as diffuse nebulae, planetary nebulae, open clusters, globular clusters, and Messier catalog galaxies, the maxim “greater openness equals better vision” is true. Another concern: The “urban aperture” myth suggests that a telescope with a larger aperture will collect excess light pollution in urban environments, thereby affecting performance. A wider aperture will indeed collect more starlight in any scenario, allowing you to view fainter objects. That said, larger apertures are more sensitive to heat currents and turbulent weather conditions and this can affect image sharpness. For our test pool we didn’t venture into the much larger 10-inch, 12-inch, or more than 14-inch apertures, which are often so large and bulky that they dissuade many people from taking out their telescope and using it as much as possible.
Magnification it is also a great consideration, and is determined by two things. The first is the focal length, or the distance (in millimeters) between the telescope’s main lens or mirror and where the light rays meet. Focal length is equal to the telescope’s focal ratio (f / number) multiplied by the diameter of the primary lens, or aperture. Focal length is the main factor in determining the magnification power of the telescope.
More magnification power means you can see smaller objects that are further away, but it doesn’t necessarily mean better image quality. At lower magnifications the image you observe may appear bright and with good resolution, while at higher magnifications the same amount of light is scattered over a larger area, resulting in a larger but more blurry image. Think about the effect of blowing up an image on your phone or computer beyond its normal size. You don’t always get the best image quality.
The second key component in determining magnification is the telescope eyepiece. To calculate the magnification power of your telescope, you need to divide the focal length of the telescope by the focal length of the eyepiece. If you put a 10mm eyepiece on a telescope with a focal length of 1000mm, for example, your magnification power will be 100x.
You can determine the magnification limits of a telescope by multiplying the diameter (in millimeters) of the main lens or mirror by 2. So a 150mm telescope, for example, would have a practical magnification limit of about 300x. As a general rule, the maximum amount of magnification desired for a telescope is 50x per inch of aperture. If you have our top pick, the Celestron NexStar 5SE, which boasts a 5-inch aperture, 250x is the highest magnification, or power, you should consider.
Contact lenses are another consideration. A Barlow lens is supplied as an accessory with many of the telescopes we have tested. This auxiliary lens system fits between the telescope and the eyepiece, decreasing the focal length of the eyepiece and offering double or sometimes even triple the magnification of the image.
All of the telescopes we tested come with a 20mm or 25mm eyepiece. Most of the models we tested are also equipped with a 10mm eyepiece. It may seem counterintuitive, but the 10mm eyepiece offers greater magnification, producing a larger image and smaller field of view.
A scope of the seeker it comes with a telescope and is normally mounted on the telescope itself. Each viewfinder has a battery operated red dot or set of sights to allow you to align and center an object in its viewfinder. Aligning the finderscope before viewing through the telescope is an essential step that will help you locate what you are looking for through the most powerful telescope.
Next, we learned about the different types of scopes. In a refractor telescope, the light passes through the lens at the front and travels directly to a mirror on the back of the telescope and then into the eyepiece. With this type of telescope it is possible to view objects both in the sky and on the ground, because the image is not inverted inside the telescope. The trade-off is that this type of telescope generally doesn’t work as well with faint objects in the sky.
A reflector the telescope uses two mirrors instead of a lens to collect and focus light. Such models typically allow for superior image quality of faint sky objects. On the flip side, reflector telescopes can collect more dust and debris in their internal components and require a little more maintenance. Dobsonian telescopes, a type of reflector model, are often referred to in astronomical circles as “buckets of light”.
A compound, or Schmidt-Cassegrain, The telescope (sometimes referred to as a catadioptric telescope or Cassegrain for short) is a combination of two mirrors and a lens. These scopes are best for viewing faint objects and can also work for viewing objects on earth.
In the end, we got acquainted with the mounts on which scopes are mounted. A altazimuth mount, or mount alt -aziumth, it is a simple system that moves both vertically (“altitude” movement up and down) and horizontally (“azimuth” movement from side to side). This type offers the best beginner experience, in terms of ease of use and scope control. These stands sometimes come with computer controls that will find objects in the sky for you.
Equatorial mounts they are more complicated and must be aligned with the earth’s axis. After doing this, the oscilloscope tracks objects in the sky as they move. This design is particularly useful for astrophotography, because it eliminates field rotation as it follows the object across the night sky.
