What is advantages and disadvantages of Refracting Telescopes ?

The Telescope

The telescope is an instrument that collects and analyzes the radiation emitted by the distant sources , The most common type is the optical telescope , It is a collection of lenses or mirrors that is used to allow the viewer to see the distant objects more clearly by magnifying them or to increase the effective brightness of a faint object .

The telescopes can operate at most frequencies of the electromagnetic spectrum , from radio waves to gamma rays , The one characteristic all telescopes have in common is the ability to make the distant objects appear to be closer .

The advantage of using a telescope in space is that you don’t have to look through the Earth’s atmosphere , For very detailed observations the atmosphere is pretty murky and horrible  , You have probably seen HST pictures , and they are much more detailed than you can get from the ground .

The disadvantages are mainly to do with the hassle of operating in space ,  It is  much more expensive , so , you can’t have such a large telescope , If the things go wrong , It is much harder to repair them , You can’t update the instruments  , So  , they quickly become out of date ,  Also with the modern technique of Adaptive Optics , the ground based telescopes are catching up with the HST .

The telescope is an instrument used to see the objects that are far away ,They are used to view the planets and the stars , Some of the same optical technology that is used in the telescopes is also used to make the binoculars and the cameras .

There are three main types of telescopes which are the refracting telescopes  , the reflecting telescopes and the catadioptric telescopes .

Refracting Telescopes

Refracting telescope

Refracting telescope

The refracting telescopes use the  lenses to bend the light to a specific focal point such that the object will be magnified to the viewer , It is the simplest type of telescope and  the most recognizable , Its design is very simple , It is essentially a tube with a lens at each end .

The basic refracting telescope has two lenses , The first lens is called the objective lens which is a convex lens that bends the incoming light rays to a focal point within the telescope , The second lens is called the eyepiece which takes the light from the focal point and spreads it out across the retina of your eye , It makes the object seem much closer than it really is .

Advantages of Refracting Telescopes

Because of their simple design , they are generally easy to use and more reliable as their optics are permanently fixed and aligned , They are superior revolving power per inch of aperture and superior performance in inferior conditions and they have image steadier .

There are not reflections or interruption of light path , there is near permanent optical alignment , minimum maintanance , and long focal ratios can mean use of longer focus , simplier and eyepieces .

The refractor telescopes are rugged after the initial alignment their optical system is more resistant to misalignment than the reflector telescopes .

The glass surface inside the tube is sealed from the atmosphere  , so  , It rarely needs cleaning , Since the tube is closed off from the outside , The air currents and effects due to changing temperatures are eliminated , This means that the images are steadier and sharper than those from a reflector telescope of the same size .

Disadvantages of Refracting Telescopes

They can be heavy especially larger aperture telescopes  because of their need for large lenses , They can also have a longer body which may impact on transportation and storage , And there is a certain amount of secondary spectrum ( chromatic aberration ) unavoidable ( the reflector completely free of this ) .

They may be more expensive as large high quality lenses are more costly to produce , The cheaper lenses are more susceptible to aberrations , They have very high initial cost relative to the reflector telescope .

All refractors telescopes suffer from an effect called the chromatic aberration that produces a rainbow of colors around the image , One way to reduce this problem is to use the multiple compensating lenses to counteract the effects of this kind of aberration .

There is another way which uses a very long objective focal length ( which is the distance between the focus and the objective ) to minimize the effect , This is why the early refracting telescopes were made very long .

There is another problem which is the shape of the lens , It is technically difficult to make a glass lens with no imperfections inside it  with a perfect curvature on both sides of the lens .

There is a second problem which is the thickness of the lens  , how well the light passes through the objective decreases as the thickness of the lens increases but at the same time , since the objective can only be supported at the ends , the glass lens might sag under its own weight .

The refractor telescopes ( as well as the reflector ones ) can suffer from a defect called the spherical abberation so that not all of the light is focussed to the same point .

How a Refracting Telescope Works

The refracting telescopes are very simple , It uses a lens to gather and focus the light ,  where the light enters through a main objective lens at one end , then the lens refracts ( bends ) the light to a point of focus at the other end , So ,  This is then magnified to form an image by the eyepiece which is inserted in the other end of the telescope , The eyepiece can be moved back and forth to adjust the sharpness of the focus .

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