The history of the telescope makes for interesting reading from a theoretical perspective, but also from the perspective of someone interested in beginning to make a telescope. During the development of the telescope, practical experiments with reflectors had already begun in 1639, but it was not until 1663 that they gained any prominence.

The Gregorian Telescope

In that year a Scottish mathematician, James Gregory, at the age of 24, published a treatise entitled Optica Promota. In this he gave a description of a compound reflecting telescope employing two concave specula (metal mirrors). The larger one was to be perforated, and to have a paraboloidal surface; the smaller was to be ellipsoidal. 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 unyielding lap was an insurmountable barrier to parabolizing, interest apparently ebbed, and about 60 years were to elapse before a workable model was finally produced.

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 .

While the Gregorian is seen to be capable of higher magnification, all that is necessary can be had from the Cassegrainian, and it has the advantage of being a much more compact instrument. Although little was heard of this telescope for the next two centuries, it is worth observing that it survived the Gregorian, and is still widely used in observatories. This is a good place to begin it you decide to make telescopes of your own.

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. His methods were ingeniously calculated to yield a spherical surface, and it is quite probable that a close approach to that figure was attained. But the performance of even a spherical mirror of the proportions of Newton's could hardly be satisfactory because of the great amount of spherical aberration present.

Although Newton thought that his mirror might fail of good definition, he "despaired of doing the work" (parabolizing the speculum), yet he "doubted not but that the thing might in some measure be accomplished by mechanical devices."

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. That is a practical solution, and the resulting surface in each instance is a paraboloid.

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. Incredible though it seems, this represents the difference between poor and good definition.

The single-lens eyepiece of Kepler's had already been improved, with the addition of another element, by Christian Huygens, a Dutch astronomer and mathematician, about the year 1650. The field lens, like Galileo's concave lens, is placed before the focal plane of the objective. As it is convex, however, it further converges the rays to form' a slightly smaller image in a new focal plane, which is then magnified by the eye lens. Thus, a much wider field of view is encompassed by the eyepiece.

These were important developments in the history of the telescope on the way to our present-day powerful telescopes. 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. Provided you have a little patience.

reflecting telescope

Getting to Know Reflecting and Refracting Telescopes

Telescopes are outstanding instruments for exploring objects in the night sky and the principal part of any telescope is the objective. The objective lens is what gives access to the light into the telescope enabling you to visualize the images from the sky. Telescopes with bigger objective lenses permit more light in and that means a sharper image for the spectator.

The 2 primary types of telescopes are reflecting telescopes and refracting telescopes. These two types are similar in overall design apart from for the manner in which they collect light.

The Key Differences in Refracting and Reflecting Telescopes

The objective lens in refracting telescopes is a glass lens that is placed close to the front end of the telescope. The objective takes the light that it collects and refracts, or deflects, it to send it to the eyepiece, which then magnifies the image. Refracting telescope engineering is also an important elementin other precision equipment like binoculars, rifle scopes and spyglasses.

On the other hand, reflecting telescopes are different because the objective lens is a reflective mirror at the bottom end of the telescope rather than a glass lens at the front end. The mirror in a reflecting telescope has a dished shape, or a bowl like shape, which permits it to capture the light in the central of the mirror and direct it as one stream of light towards the eyepiece so the image can be viewed.

Reasons to use a Reflecting Telescope

Reflecting telescopes are desired by many astronomers for various reasons. A key reason is less distortion with a reflecting telescope than with a refracting telescope since the mirror is able to gather and reflect all wavelengths of color consistently. The utilising of the mirrors instead of glass lenses reflecting telescopes less expensive than refracting telescopes.

When mirrors are utilized rather than glass lenses, the telescope can be designed much larger to allow for the supports for the mirror to be located on the posterior of the telescope. The larger the mirror that is used, the more light that is reflected and the better and clearer the image will be.

Disadvantages of the Reflecting Telescope

Reflecting telescopes can have their own issues and problems as well. One problem can be the size of reflecting telescopes. As larger and larger mirrors are used, the telescopes have to grow in size to fit the mirrors inside. While the images are better with the larger reflecting telescopes, they are not very portable and it can be problematic finding a a convenient place to keep them when you are not using them.

Another problem is that reflecting telescopes may require to have the mirrors alignment corrected from time to time to keep them working perfectly and to maximize the light that is captured.

Many of the most popular telescope brands provide both refracting and reflecting style telescopes for the unprofessional stargazer.

Virtually all of the better telescopes used in research are reflectors. Reflecting telescopes come in many design variations and may utilize complementary optic elements to improve the image quality or position the image in a mechanically advantageous position. As reflecting telescopes utilize mirrors, the design is often referred to as a catatropic telescope.

refracting and reflecting telescope

At one point in time, the stars and the moon held mysteries that mankind could only guess at. Knowledge only came with observation and study, yet this was nearly impossible when the objective was far away. By providing magnified views of distant objects, telescopes allowed mankind to learn about the night skies and the planets around us.

Other areas of study, including land and sea navigation, have prospered from the invention of the telescope. Binoculars, microscopes, camera lenses, and binocular spotting scopes, binoculars cameras , monoculars to name a few, are all here today because of telescopes.

telescopes
The earliest known telescope was created in 1608, and Galileo Galilei built his in 1609. Galileo is credited with the first astronomical uses of the telescope. Initially, it was used to spot ships. Johannes Kepler further improved upon Galileo's design in 1611. From its modest creation from a pair of lenses, the telescope of today bears little resemblance to its ancient ancestor.

The telescope falls into three categories: reflecting, refracting and catadioptric. A reflecting telescope uses an arrangement of mirrors, a refracting telescope uses an arrangement of lenses, while a catadioptric telescope uses a combination of lenses and mirrors.

Telescopic research is an area where technology has advanced. When presented with the limitations of the refracting telescope, development of the reflecting telescope commenced. Initially designed in 1616, it wasn't until 1668 that Sir Issac Newton developed the first practical reflecting telescope.

compact binoculars
As with other telescopes, the larger the primary reflector, the better the image will be. Today's optical systems range from less than 2 meters to over 11 meters. Unfortunately, the atmosphere of the earth limits the effectiveness of ground based systems because of atmospheric distortion. Several solutions to this problem have been found, including the Hubble Space Telescope.

Since its beginning in renaissance Venice, the telescope has assisted or directly contributed to numerous advances or discoveries. Ocean navigation depended upon it. Astronomy was born from it. Cameras were developed from it.

Just to name a few. And we haven't finished learning yet. There is still a lot left to learn about these miraculous inventions, and mankind has, and will continue, to benefit immensely from these discoveries.

binocular rangefinders
Technology keeps improving telescopes and other optical systems. This new technology will push for the development of additional orbital platforms, which will help to eliminate atmospheric distortion plaguing other telescopic systems.

Newer optical systems are in the works that can correct for atmospheric distortion. When you think about how far the telescope has come from its initial, humble beginnings, it is an amazement unto itself.

In the world of astronomy, different types of telescopes are used to view the stars and planets. However, it is the refracting and reflecting telescope that represent the two basic types of telescope used by today's novice and professional astronomers. Of these two telescopes, the refracting telescope has the longest history and has been in use for centuries. Its design was developed around the 15th century and is still a very popular telescope in the twenty-first century. Actually, a refractor telescope is one of the oldest telescope designs still in use by today’s astronomers.

The Workings of a Refracting Telescope

The refracting telescope, sometimes referred to as a refractor telescope, consists of multiple concave lenses which allow the incoming light to be refracted, resulting in images that are brighter and larger. These qualities make the actual images appear much larger than viewing with the naked eye. These refractors gather the incoming light and bend it, allowing you to view objects from a distance. This magnification is what provides you with the ability to clearly view the stars and night sky. Even though refracting telescopes look complicated, the truth is that they are basically a series of concave lenses that refract the light.

The Benefits of a Refracting Telescope

The refracting telescope has a long history, with centuries of use and design enhancement. Over time, its design was repeatedly tested, resulting in continuous improvement of its design and magnification capabilities. This was a real benefit providing astronomers with the opportunity to determine the refracting telescope design’s strengths and weaknesses.

The refracting telescope has obviously been improved dramatically since the fifteenth century. Even with the improvement of refractor technology, it is the size of the refractor telescope that still poses a potential concern. As the need for increased magnification has presented itself, the refractor lens has become larger. This can result in a larger risk of defects or sagging.

The truth is that refracting telescopes have proven themselves across the centuries and, to attest to their value, have remained one of the most popular designs among astronomers. Regardless of the type of telescope you choose to scan the cosmos, the ongoing use and popularity of the refracting telescope provides assurance that it will be with us for decades to come.

Buying a Refracting Telescope

If you are like most budding astronomers, it can be confusing trying to select the best refracting telescope for the money. But what we found was that visiting telescope and astronomy websites that provide telescope reviews can be very helpful in making your decision. So, whether you are considering a beginner telescope or professional model, be sure to do your research and you will be assured of enjoying many hours of star gazing pleasure.