In 1733, the achromatic lens was invented by Chester Moore Hall, an English barrister. He began to make a telescope in the early 1700, but this was accomplished by combining a convex crown and a concave flint lens in such a way that their focal lengths were inversely proportional to their dispersions.

Although a number of telescopes were made according to Hall’s instructions, the benefits of the achromatic lens do not appear to have been made available to the public until John Dollond invented it independently in 1758, and patented it.

Dollond’s efforts led to a demand for clearer glasses of more varied densities and of less equal dispersions, needed to improve achromatism, and chemists pursued experiments in learning how to control the refractive indices of melts, and in the pouring of large disks of limpid, homogeneous glass.

Altogether, excellent progress began to be made, and by 1800 achromatic objectives 6″ in diameter were being turned out. Some of the best glass had been manufactured by Guinand, a Swiss who worked with Fraunhofer from 1805 to 1814. Fraunhofer produced a number of splendid achromats up to 9″ in diameter.

Dollond began to make telescopes of the refractors variety (spyglasses) with single-lens objectives as early as 1742, his price for a 2-foot telescope then being 7s 6d. In comparison, in 1762 he sold a 2-foot telescope with a two-lens objective (achromat) for 2 guineas. The lens diameters in each case were just under 2″.

In 1783, with a view to combining the benefits of the wide field of Huygens’ eyepiece with a means of making micrometric measurements of an image in the focal plane, Jesse Ramsden, an English optician, designed the compound eyepiece. Building a telescope was becoming more like the process undertaken today.It can be seen that a measuring device, such as adjustable parallel wires, set in the focal plane would be magnified along with the image. Measurement of an image in the focal plane was by no means a new idea; probably this had been first accomplished by Gascoigne, an Englishman, about 1638.

With the advent of the achromatic lens, the erecting or terrestrial eyepiece assumed considerable importance. This type of eyepiece was first suggested and used by Kepler, and improved in design about 1645 by Antonios Maria v. Schyrle, a Capuchin monk better known as Rheita. It is mentioned here because it spelled the rise of the refractor and the decline of the Gregorian for terrestrial use.

In the early part of the 19th century, small achromatic refractors were being manufactured by several concerns. For those not having the means to buy achromats, telescopes with single-lens objectives continued to be made. Enterprising opticians were also offering lens sets that could be assembled into simple refractors.
The Modern Era

The method of chemically depositing silver on glass discovered about 1840 by Justus von Liebig, of Nuremberg, was successfully applied to a small glass telescope mirror in 1856 by Karl Steinheil, a German physicist, and independently in the following year by Jean Foucault, the famous French physicist.

Various processes of plating glass with metal for the making of mirrors had been known and practiced for centuries, but for one reason or another, the coatings were unsuited for front-surface reflection. There became many ways to make telescopes.

Then, in 1858, Foucault announced the development of his amazingly delicate and simple test for a concave reflecting surface, using an illuminated pinhole and a straightedge placed in the vicinity of the center of curvature of the mirror. The pinhole and straightedge were the outgrowth of earlier experiments in which simultaneous microscopic comparison was made of a pin point, likewise placed at the center of curvature of a mirror, and its reflected image, which was caused to fall alongside.

The last speculum of note to be constructed was one four feet in diameter, made by Grubb in 1870 for the Melbourne Observatory. Silver-on-glass mirrors replaced the more expensive and difficult-to-work speculum. It tarnished, but not nearly so quickly as speculum, and it could be removed by chemical means and a new coating applied without upsetting the figure of the glass surface.

Building a telescope was becoming closer to being constructed in the style we know it today.

Some of these instruments are portable, and others must be mounted on a solid pier. The amateur, however, usually will have formulated no particular plan of observation, except a desire to explore the heavens, and to see with his own eyes some of its wonders.

From the experience gained by amateurs who make telescopes, it has been found that the most practical and popular instrument for amateur use is the 6-inch f/8 Newtonian reflector.

Its concave mirror is 6″ in diameter and its focal length 48″. The delicate task of parabolizing the mirror, while not easy, is not beyond the ability of a careful worker. The 4-foot focal length makes for comfortable observing, and with a low-power eyepiece, the field of view is a trifle over one degree in diameter – more than twice that of the full moon.

The magnifications that may be employed permit of a modest size of mounting, which can be made portable. Such a telescope should reveal stars of magnitude 12.8, as compared with the 6th-magnitude limit of the unaided eye, and the 9th-magnitude limit of the average small binocular.

Theoretically, the mirror is capable of resolving double stars having a separation of % of a second of arc, but as magnifications exceeding about 30 per inch of aperture can seldom be used, it may not be expected to perform up to this limit. When you make telescopes of this kind they will show the divisions in Saturn’s rings; surface markings on the moon little more than a mile across should also be visible.

The purchase price of such an instrument of professional make is necessarily high, and many an amateur feels compelled to do without it. But if he is possessed of some ingenuity and craftsmanship, and is willing to devote a few hours a week to the task, he can in a relatively short time build the telescope in its entirety, for a small fraction of that price.

Of course, many who make telescopes feel that their mirrors are inferior to the professionals’, but this is not necessarily true. It has been frequently demonstrated that mirrors of professional make will seldom stand up to a test, because it is impossible for the professional optician to spend sufficient time on the mirror without losing money, whereas the amateur can, if he will, devote all the time and care necessary to produce a mirror of admirable figure.

Upkeep is slight in amateur telescope making. The reflective aluminum coating of the mirrors of a reflector is subject to deterioration from dust and the elements admitted by the open tube, but given the same protection when not in use that is accorded a refractor, at least two years of service should be realized before the aluminizing job need be repeated.

For those who decide to make telescopes, the task is time consuming but extremely rewarding. Good luck!

Very early in the 19th century, when advocates of the speculum mirror began to feel the challenge of the refractor, Dr. Nevil Maskelyne, English Astronomer Royal, ventured the opinion “that the aperture of a common reflecting telescope, in order to show objects as bright as the achromat, must be to that of an achromatic telescope as 8 to 5.”

The relative inefficiency of the reflector of that day was due to the fact that, even under most favorable circumstances, barely 40 per cent of the original light escaped absorption by the metal mirrors, the greatest losses occurring in the short and medium wave lengths. Even silver-on-glass mirrors are subject to considerable deterioration, especially under certain conditions of the atmosphere.

The reflectivity of aluminum, however, is more-or-less constant, and from a standpoint of image brightness, it placed the reflector on a more equal footing with the refractor. In fact, until the quite recent development of anti-reflection lens coatings, an aluminized mirror has had the same efficiency, in light-transmitting qualities, as an air-spaced achromatic objective lens of equal aperture.

Coming down to figures – due to reflection there occurs in an untreated lens a light loss of slightly more than four per cent at each of its surfaces.

With reflection losses to be accounted for, plus an absorption loss in the substance of the glass (amounting to about two per cent for lenses of moderate size), it is evident that about 82 per cent of the original light is transmitted. In the reflector, after first deducting that area of the mirror’s surface obscured by the diagonal, an equal percentage of the original light is found to be transmitted.

Of course, this transmitted light is subject to another reflection by the diagonal, but the refractor will probably employ a star diagonal, the function of which is similar to that of the diagonal or prism of the Newtonian, so an equivalent loss may occur there. Therefore, for those engaged in amateur telescope making, with either instrument, the same amount of light reaches the eyepiece.

It was discovered, however, in the latter part of the last century by those who make telescopes, that some lenses which had been tarnished by the elements transmitted more light than ones that were newly polished; it was found that this resulted from lessened reflections at the tarnished surfaces. Various processes of producing an artificial tarnish were attempted. At present, in the most satisfactory method, metallic salts (such as magnesium fluoride) are evaporated in a high vacuum onto the glass. Ideally, the refractive index of an anti-reflection fluoride coating should vary from that of glass at the glass-fluoride surface to that of air at the fluoride-air surface, in which case no reflection would occur.

Practically, the index of the coating should be equal to the square root of the index of the glass, and its thickness equal to a quarter of a wave length of yellow-green light. Only the light at opposite ends of the visible spectrum is then reflected, amounting in general to less than one per cent of that of the whole, and is detected by the purplish color given to the reflection.
From the standpoint of an introduction to the optician’s trade, the experience of thousands of amateurs has shown that one’s teeth should first be cut on at least one good mirror. Then, if a refractor is contemplated, additional experience can be gained by making the optical flat that is so essential in the testing and figuring of the objective lens.

For beginners it would seem that the first step to make telescopes is to make a reflector.

The Gregorian Telescope

High magnification could be had with this instrument, the second reflection amplifying the focal length of the primary in the ratio of fs to Fs.

He began to make telescopes, but whatever chance it may have had of performing creditably was lost by polishing the speculum on a cloth lap – putty (tin oxide) being used as the polishing agent. The Cassegrainian Telescope Sieur Cassegrain, a Frenchman, in 1672 designed a second compound reflector, differing from Gregory’s in that it employed a convex secondary, to be of hyperboloidal figure, placed inside of the focus of the paraboloidal primary .

The Newtonian Telescope

The history of the telescope takes an interesting turn at this point. In the same year, Newton designed and began to make telescopes that had two small reflectors, of the type so popular with amateur astronomers today and which still bears his name. They were not large, as we know telescopes today, the effective apertures of the concave specula being about 1 1/3″. Their focal length was 6″, making the focal ratio f/4.5.6

Newton, according to his Opticks (1704), polished his specula on pitch, using putty as the polishing agent. It might be concluded that if the center of the mirror were properly deepened, that is, given a shorter radius, or if the radii of the outer zones were progressively lengthened, or if a little of each were done, all the reflected rays could be brought to a common focus. The standard practice is to deepen the spherical mirror so that, for a 6-inch f/8 mirror, the glass removed in the operation is but half a wave length of light in thickness at the center. The field lens, like Galileo’s concave lens, is placed before the focal plane of the objective.

Ever since Galileo took a Dutch invention and adapted it to astronomical use, astronomical telescope making has been an evolving discipline. Many astronomers after the time of Galileo built their own telescopes out of necessity, but the advent of amateurs in the field building telescopes for their own enjoyment and education seems to have come into prominence in the 20th century.

Today telescopes of the size and technicality used by NASA experts are out of an amateurs grasp (and price range), but an amateur can easily begin to make telescopes of the kinds mentioned above both inexpensively and easily.

What Type of Kid Telescope Should You Consider?

With fewer moving parts and a simplistic, well-crafted design, the reflecting telescope design has been highly recommended by some experts as one of the best beginner telescopes. Others believe that an easy-to-use reflecting telescope is the better telescope for novices. In making your decision, a good source of information is the telescope user reviews found on many online telescope websites. But, whatever your choice, select the model that is tailored for new telescope users and one that can be set-up quickly and can be aligned and operates easily.

While a kid telescope cannot offer custom or state of the art optics, ones from reputable manufacturers are generally quite satisfactory. A word of warning though — It is generally best to avoid “department store” telescopes. These are generally of lower quality and designed for mass production at the expense of quality.

Why You Should Start with a Kid Telescope

The reasons we suggest that you start on a smaller scale is that you want to avoid the frustration of attempting to use an advance telescope without training and experience. A beginner telescope will afford you with a great number of opportunities to view the stars and planets while you learn the basics of stargazing. Prices for a kid telescope can be as low as $200 or as high as $2,500, but we would suggest that you look for telescopes in the $300 to $600 price range.

So if your novice astronomer is ready to start on their journey to the stars, take a “right” at the Sea of Tranquility and fly yourself into deep space by visiting the Crab Nebula. Its really easier than you think, thanks to the strong magnification , precision optics and simple operating controls of the kid telescope .

The name “telescope” is actually a combination of two Greek words, tele which means ‘far’ and skopein which means ‘to look or see’. Hence the blending of these two words would be teleskopos which means ‘far-seeing’.  Telescopes are in fact used to view astronomical objects which cannot be seen through the naked human eye.

Telescopes cover a wide range of instruments which are designed for the observation of remote objects. Hence, telescopes can in fact, refer to a whole gamut of instruments.

Ideally, a telescope is used to view distant objects, but the area of application can vary greatly.

The classifications of telescope essentially vary depending on the construction and the working. Since the usage of the telescope largely depends on its working, when the working varies, the purpose for which it is used also varied greatly.

If you are looking to buy a telescope it is necessary to understand the purpose for which you want to use it. Otherwise you would end up with a room filled with a variety of telescopes, without using any of them.

Why do you want to buy a telescope?

Do you want to pursue astronomy as a hobby? Do you want to provide a significant learning experience to your child? Or is it just a something that you wish to carry along with you camping gear for your camping trip?

If your intention for buying a telescope is just focused on one particular event like your camping trip or too see if you kid has imbibed the same proclivity towards star gazing as you have, then you can probably settle for a light weight, small budget telescope or a binoculars as well.

How much do you want to spend on your telescope?

The answer for this question is usually interlinked with the purpose for which you want to buy a telescope. If you are looking for a telescope for a purpose that is even-driven or ephemeral, then investing in a telescope which costs a bomb is not worth. You might want to buy something small and not too expensive. You can also consider buying one of those toy telescopes, if it is to check on the inclination your kid has towards astronomy.

If you spend a humungous amount of money on buying a telescope that’s large and complex and you don’t use that very often, then it won’t be of much fun.

Some advice before investing for a telescope:

Before you invest in a telescope you might want to join an online club or the astronomy club in your locality. Joining a club will even help you in networking with fellow astronomers who can guide you on the type of telescope to buy that suits your purpose as well as your pocket.

You can even subscribe to a few journals on astronomy or read up on the internet about the technical details on astronomy so that you can identify a few constellations or spot a planet or two with your naked eyes. Getting yourself familiar with a few astronomical words would also be helpful.

Therefore consider the purpose and the budget before investing in a telescope.