The optimal telescopes are instruments used to gather and focus light
from a visible portion of the electromagnetic spectrum. They are usually
used in viewing a magnified object in making a photograph and in
gathering data through electronic image sensors. Wavelengths of light
are then magnified and placed under study.|
There are three types of optical telescopes identified. First, we have the refractors, also known as the dioptrics. Refractors make use of lenses. There are also the reflectors or the catoprics, which use mirrors. A combination of mirrors and lenses is called catadioptrics.
How They Function
So how do these optical telescopes basically work? All optical telescopes have this major light-gathering source. In refractors, it is called the primary objective lens. For reflectors and catadioptic designs, it is the primary mirror. This source gathers the incoming light from a distant and isolated object and focuses it back along a path called the focal plane.
As the light beams re-converge, a focal point is reached, and a "real image" is formed. This image is then gathered by the telescope's photo sensors and magnified by a series of lenses called the eyepiece. The eyepiece here acts as a magnifying glass, and the human eye sees the already magnified virtual image of the target object.
How They All Started
The first record in history of optical telescopes was in 1608. That year in Netherlands, the invention of the equipment is credited to spectacle inventors Hans Lippershey, Zacharias Janssenin Middelburg, and optician Jacob Metius. However, the lens and the principles of refracting and reflecting light have been known since the beginning of recorded human history. Greek philosophers were said to develop and preserve the theories in the foundation of optical telescopes. Developments in the manufacture of lenses and spectacles were even recorded in the thirteenth century in Venice and Florence, Italy. After a few years, it was brought to Germany and Netherlands.
Galileo Galilei is acknowledged as the first to use optical telescopes in the field of astronomy. The Galilean telescope was based on Hans Lippershy's design of a convex objective lens and a concave eye lens. Johaness Kepler then developed and proposed an improved version of Galileo's telescope, which used a convex eyepiece. It was called the Keplerian Telescope.
The first practical reflecting telescope was developed in 1669 by Isaac Newton. However, it took more than a hundred years for the reflectors to become popular because of the difficulty in the construction of the equipment and poor performance of its speculum metal mirrors.
Several advances followed suit in the eighteenth century like the perfection of the parabolic mirror fabrication and the silver-coated glass mirrors in the nineteenth century. Long-lasting aluminum coatings, segmented mirrors, and active optics were then introduced in the twentieth century. The catadioptrics came in the mid-twentieth century, and was mainly used for wide field imaging without spherical aberration. Adaptive optics and space telescopes were then used in the late twentieth century.
Famous optical telescopes include the Hubble Space Telescope and the Keck telescopes, which is currently the largest in the world.