The refracting telescope was invented in 1608 by Dutch lens maker Hans Lippershey (originally for military purposes), and the following year Galileo Galilei became the first
astronomer to use it to observe the skies. In a rafracting telescope lenses are employed to collect and focus light coming from the outide. Light enters through the objective lens (the big lens at the end of the scope), and focuses down the length of the primary telescope tube. At the end of the telescope, an eyepiece lens then magnifies the resulting image. Refractors are relatively uncomplicated machanisms compared to some other types of telescopes, which makes them a good choice for beginners (although they can be expensive compared to telescopes with similar capabilities). Refractors have what are known as long focal ratios. Focal ratios are determined by dividing the diameter of the objective lens (or mirror for other telescope types) by the distance it takes the lens or mirror to form an image.
Instead of lenses, reflectors use mirrors to collect and focus light. Light enters the telescope at the front and hits the curved, parabolic mirror at the back of the telescope, which sends it back towards a second, smaller flat mirror close to the front of the scope. This secondary mirror then sends the light to the eyepiece lens, which then magnifies the resulting image. The first reflector telescope design was by Sir Isaac Newton and most reclectors that are used by amateurs are Newtonians.
Reflectors are generally inexpensive compared to other types of telescopes. Some of the drawbacks include the fact that they're not very useful for looking at anything other than the sky, and the fact that, thanks to an open tube, reflectors are liable to gather dust and imperfections over time, which will compromise image quality.
Catadioptrics use both lenses and mirrors to collect and focus light; two of the most popular variations of this type of telescope are Schmidt-Cassegrains and Maksutov-Cassegrains (these two types differ in the type of corrector lense that is used at the front of the cope to increase the field of view). These telescopes inhabit a middle ground between reflectors and refractors in terms of price and focal ratio, and most offer the additional advnatage of being relatively compact, and therefore, somewhat easier to log from place to place.
Choosing your telescope
Which of these telescopes is best for you will depend on what you want out of your night sky experience. Those who like looking at planets should go for a refractor, while those fascinated with clusters and deep sky objects will be better off with a reflector. In the absence of of a preference on way or the other, a catadioptric tekescioe will provide you with the greatest flexibility.