There are a few basics in choosing a telescope for a beginning astronomer, although there are many factors that go into quality and price of a telescope. As with anything else, you get what you pay for.
A good telescope will not talk about its “Power”
Lower power provides a better view experience since many high powered telescopes makes an object appear larger and light gathered by the scope is spread over a larger area creating a fainter image therefore, limiting how much of the large image you can actually see.
REFRACTOR & REFLECTOR EACH HAVE ADVANTAGES AND DISADVANTAGES
– have a totally clear aperture allowing light to be scattered from brighter to darker areas, making the contrast is better and the preference for planetary and double star observing.
– another advantage is low maintenance. Lenses don’t require recoating and the optical tube assembly typically does not require collimation since the lens is fixed into the tube and does not become misaligned.
– it may require a longer cooling time to ambient temperature although newer technology’s thin-walled aluminum tubes have reduced the cool down period.
– another disadvantage is some chromatic aberration in bright images, which is more evident in achromatic refractors.
– the primary disadvantage of refractors is cost, due to the expense involved in producing a large achromatic or apochoromatic lens.
– they do not develop chromatic abberation.
– the secondary mirror creates what is called a “central obstruction.” This causes some scattering of light and loss of contrast in the viewed image.
– another disadvantage is ease of misalignment, need for frequent cleaning and possible spherical abberation.
APERTURE SIZE IS THE TRUE KEY TO THE “POWER” OF A TELESCOPE
You’ll want at least a 4″ wide aperture for deep-space viewing, 2.4 inch (60mm) and 3.1 inch (80mm) refractors and 4.5 inch and 6 inch reflectors are popular for most amateurs.
KNOW A TELESCOPE’S FOCAL RATIO
A higher focal ratio does not always mean a higher quality image. However, a higher focal ratio with the same size aperture means a longer scope, which means problems transporting it.
The focal ratio is calculated by dividing aperture size into its focal length. The focal length is measured from the main lens (or mirror) to where the light converges to focus.
A GOOD MOUNT IS NECESSARY FOR STEADY VIEWING
Some kind of stand to hold the scope steady is essential. It is extremely difficult, if not impossible, to view a distant object if the scope is not very steady.
POWER IS NOT THE OBJECT WITH EYEPIECES
The telescope should have at least 1 eyepiece and is rated by millimeters (mm), with smaller numbers indicating higher magnification. A 25mm eyepiece is common and appropriate for most beginners.
A higher power eyepiece does not mean better viewing. Higher and lower power eyepieces each have their place.
A higher magnification eyepiece provides more details, but it may be harder to keep an object in view, unless you are using a motorized mount. They also require the gathering of more light to provide a clearer image.
A lower magnification eyepiece makes it easier to find objects and keep them in view, requiring less light, so viewing dimmer objects is easier.
Don’t forget to include books on amateur astronomy and star charts to make the gift of a telescope more enjoyable.