While the unaided eye or binoculars can reveal much of the night sky, a telescope reveals much more. Seeing the rings of Saturn or the craters of the Moon with your own eyes can be an “oh wow” moment. However, choosing the right telescope can be tricky. There are binoculars with lenses and binoculars with mirrors.
Hand-operated telescopes and others electronically controlled. Binoculars come in many sizes, a trade-off between light-gathering power, portability, and cost.
While there's a lot to consider, changes in pricing and technology have made spectacular views of the universe more accessible than a decade ago.
How big should the hole be?
Aperture base for telescopes. The larger the light-gathering lens or mirror, the dimmer the objects you can see. Double the aperture from 50mm diameter to 100mm diameter and the light gathering area quadruples.
Aperture also limits the amount of detail you can see due to diffraction (interference) of light.
Again, bigger is better – a larger aperture telescope will produce sharper images than a smaller aperture telescope of comparable design. Earth's turbulent atmosphere also blurs images, reducing the detail seen when the aperture is greater than 150mm.
Sometimes cheap binoculars are advertised with magnification, but a small binocular with extreme magnification will magnify blurry images without revealing much detail.
Refractory or reflective?
Should you buy binoculars with a refracting lens or reflecting mirror? It depends on what you want to see and your budget.
Refracting telescopes
Refracting telescopes are good for viewing objects on Earth and in the sky. Binoculars with shorter focal lengths are more compact in refraction (where light is concentrated near the lens) and are good for low-magnification shots, which are great for sweeping dark country skies.
However, there are catches. While 70mm aperture refracting binoculars are more affordable, larger refracting binoculars are often more expensive than comparable reflecting binoculars.
Refracting telescopes are also affected by chromatic aberration – where different colors are not in common focus – and this is particularly noticeable at high magnification when stars acquire colored halos. This can be mitigated by using complex lens designs, but it increases the cost.
Reflecting telescopes
Reflecting telescopes use mirrors to focus light. These are large and do not suffer from discoloration.
Dobsonian binoculars have a simple Newtonian optical design and wooden mounts, and are a very cost-effective (if sometimes bulky) option for large apertures. Schmidt-Cassegrain and Maksutov telescopes use a combination of lenses and mirrors that are very compact (a big plus), but very complex and expensive.
How to find objects in the sky? Depends on the load
Want to see a celestial object? Point your telescope in the right direction, hold it steady, and follow the object as it moves across the sky (due to Earth's rotation).
To do this, a telescope requires a mount, which is often sold with the telescope, but can also be purchased separately. Mounds fall into two broad categories.
Equatorial mounts have their axis aligned with the Earth's axis, so a motor can compensate for the Earth's rotation. These mounts were necessary for taking long exposure images with telescopes before computers and were relatively heavy.
Alt-azimuth mounts have a vertical and horizontal axis (for example, how a camera is mounted on a tripod), and are cheaper and lighter than equatorial mounts. With the advent of cheap computing, they are now used to automatically identify and track celestial objects.
You can manually move a telescope to point it at celestial objects, or you can use electronics, including „goto” mounts with motors that turn the telescope for you.
A purely manual telescope is cheaper than a telescope with automation, but you have to navigate the sky yourself.
Electronic aids to navigation in the sky are growing rapidly and are becoming cheaper. Many telescopes on the market now use GPS and a smartphone app, which simplifies the process and makes everything even more compact.
Do I need a finder scope?
Regardless of how you point your telescope, a 30-50mm aperture auxiliary „finder” scope is useful for smaller telescopes and essential for larger telescopes.
Larger telescopes typically see a smaller portion of the sky, which makes finding your way around tricky. A finder scope with a wide field of view and crosshairs makes things easier. Even telescopes with gotoelectronics often need to be calibrated with bright stars, and finding them is easier with a scope.
What about eyelashes?
An essential part of most binoculars is your viewing eyepiece. Sometimes decent binoculars are sold with very cheap eyepieces, but it's relatively inexpensive to upgrade to a better one.
Low magnification eyepieces for sweeping views and high magnification eyepieces for planets are a good start.
Plössl eyepieces are affordable and offer good visuals. More complex eyepieces are also available that offer better visuals and are much cheaper than before.
If you want to look at the sun, you need to get a specially designed solar filter. Never point a telescope (including a finder scope) at the sun without filters – it can permanently damage the eyes and distort the lenses.
What if I want to do astro photography?
Taking basic astronomical photos has become much easier with smartphones. You can hold the phone in the telescope's eyepiece for a photo of the moon or a planet, and you'll get better results with an adapter that keeps your phone secure.
Of course, great pictures can be taken with astronomical cameras that can take very short exposures (for planets) or very long exposures (for faint nebulae and galaxies). For long exposures, automatic tracking of celestial objects is necessary and adds to the cost of the telescope.
Smart binoculars are a relatively recent addition to the market. These Goto telescopes do not have eyepieces and only capture images electronically. Because modern detectors are more sensitive than our eyes, they can capture very impressive images with a relatively small handheld telescope, even with light pollution.
However, you are missing out on the experience of seeing the universe directly through your eyes through the eyelids.
Try before you buy!
If there is a local amateur astronomy community, you can sign up or attend a star party. There are plenty of telescopes to be had, and owners delight in waxing lyrical about them.
Even a specialty store can provide hands-on experience of the telescope: its size and how it works (with limitations during daylight hours). For example, you may find that a telescope is too bulky or technical for your needs.
Online shopping can save money, but may have less customer support than a local store. You can bargain second-hand, and a seller may let you test their telescope on the moon and planets before buying.
There are many things to consider before buying binoculars. Aperture, size, cost and other factors must be considered. But there are many good options, and with a good selection you can find some amazing things. Maybe an „oh wow” moment.
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