The telescope is the oldest instrument used by man for observing the sky. The telescopes are tools to magnify images of distant objects, such as the stars. The telescope is a set of devices used for the study of the universe through the collection of electromagnetic radiation from celestial bodies like the sun, the stars and other stellar phenomena.
The use of optical instruments date back to the thirteenth century, but telescopes were invented by Dutch opticians in the early seventeenth century.
The first scientist who used the telescope was Galileo Galilei (1564-1642), an Italian inventor. The use of this instrument allowed Galileo to see four satellites of Jupiter. He had a simple 30 mm refractor telescope which had a very poor optical quality with which he observed the four satellites of Jupiter (now known as the Galilean satellites in his honor).
Currently there are different types of telescopes which are highly specialized and work in different ways.
There are basically three types of telescope to choose from; viz;
(b) Reflector and
(c) Catadioptric telescopes.
Each telescope type has its own merits and demerits, which you should consider when making a choice, depending on your lifestyle and observation purposes.
This is the oldest telescope model and therefore, the best known. It is sometimes also called Galilean telescope. This type of telescope has a long and relatively thin tubes with the main lens (objective) in front, which collects and focuses light. At the other end is where the eye can see the image. The refractor telescope is often called the bezel.
The simplest type of astronomical telescope has two lenses. Both are convex; that is, they are thicker in the centres than at the ends. The lens that is closer to the object is called the objective lens. Light from a distant source passes through the lens and reaches a focus as a ”real” and inverted image inside the telescope tube. The eye lens magnifies the image formed by the objective lens.
The refractor of all types require little or no maintenance. They have closed tubes that protect them from dust and reduce image degradation caused by air currents.
If the lenses are good, refractor telescopes give a good high-contrast image. They are especially desirable for viewing the moon and planets.
The refractors generally have small openings, typically between 60 mm and 120 mm. For many astronomical purposes, this aperture is very small. Little bright objects like galaxies and nebulae will appear as weak blurs when you can actually detect them.
Another disadvantage of these telescopes is chromatic aberration. It occurs due to the fact that the lenses have different refractive indexes for different wavelengths of light. Obviously, the larger the lens the better. However, this type of telescope becomes much more expensive as the lens size increases.
A good refractor telescope also costs more per inch opening than any other type of telescope.
The reflector is also known as the Newtonian telescope. These use a large, heavy concave mirror instead of lenses to collect and focus light. You look through the eyepiece located at the side of the tube near the top.
The light from distant objects come into the telescope tube in parallel rays, which are reflected in the concave mirror to a flat diagonal mirror. The diagonal mirror then reflects the light through an opening in one side of the telescope eyepiece lens.
Compared to other telescopes of the same opening, a reflector telescope is the cheapest telescope. An added advantage lies in the fact that the reflectors work with mirrors instead of lenses, hence, they do not have the problem of chromatic aberration as is the case with refractor telescopes.
They are bulkier than refractors and their management is less intuitive, since the eye is located near the mouth of the telescope.
Its optical quality is often less than that of refractors. However, recent models have more impressive optical qualities.
The catadioptric telescopes consist of a lens that is placed at the end of the telescope through which the light passes through first and then reaches the primary mirror at bottom of tube which, in turn, reflects the light to a secondary mirror. It tries to solve the defects of the previous telescope designs. It is pretty much a blend of the refractor and reflector telescopes.
They are short and heavy but easy to transport because of their short length tubes. These telescopes are very portable, even for those with considerable openings. For the same opening, these are shorter telescopes than reflectors and refractors.
Its optical quality is good but it fail to outperform a good refractor telescope. The focusing mechanism can be very delicate and inaccurate. They are more expensive than the reflector telescopes of the same aperture.
When buying a telescope, one must take into account many other factors such as the saddle, weight, size, place of observation and of course, the price.
Telescopes developed by reputable brands such as Celestron, Orion, and Sky-Watcher make excellent products that very durable and given you the “stepped up” vision needed to explore the night skies and see the wonders of outer space.