Table of Contents
- What is an Optical Telescope?
- Optical Telescope History
- Optical Telescope Facts
- Optical Telescope Properties
- Optical Telescope Types
- Lesson Summary
People use optical telescopes for many applications, such as astronomy, hunting, navigating and bird watching. But what is an optical telescope? The optical telescope definition is: a telescope for the visible part of the electromagnetic spectrum. So, what is a telescope? A telescope gathers and focuses light to create a magnified image of an object. Telescopes exist for all parts of the electromagnetic spectrum. There are radio telescopes and x-ray telescopes, along with optical telescopes.
Optical telescopes collect incoming light using an objective. The light is then focused to a point using lenses, mirrors or both. The focused light is then viewed through an eyepiece. There are three primary types of optical telescopes, based on how light is gathered and focused. These are
The earliest telescopes relied on lenses for magnification. The use of lenses in this way dates back to the Ancient Greeks but it was not possible to manufacture good quality lenses. It wasn't until the invention of eyeglasses in the 13th century that widespread manufacturing of lenses for this use began.
The first optical telescope was built in 1608 by a Dutch eyeglass maker named Hans Lippershey. This telescope was a refracting telescope and was composed of a convex and a concave lens. This telescope only produced a three times magnification of what was being viewed. Rapidly following this, the optical telescope spread through the Netherlands and Europe.
In 1609, Italian astronomer Galileo Galilei began constructing his own telescope. His telescope consisted of a convex objective lens and a concave eyepiece. He spent several months refining and improving his design and was able to increase the magnification from three times to 23 times. Galileo then began making astronomical observations with his telescope. He discovered the moons of Jupiter, observed the topography of the moon and tracked sunspots. In this way, Galileo revolutionized astronomy.
Some interesting telescope facts include:
The important features and properties of a telescope are:
As mentioned above there are three primary types of optical telescopes. Refracting telescopes were the first telescopes to be built. They gather and focus light using lenses. Reflecting telescopes use mirrors to gather and focus light. While catadioptric telescopes use a combination of lenses and mirrors.
The earliest kind of optical telescope was a refracting telescope. These use one or more lenses to refract the incoming light.
These telescopes work on the principle of refraction. When light passes from one medium to another with a different density, it refracts or bends. Light entering the telescope passes from the air to the lens, called the objective lens, and is refracted, focusing it on the eyepiece. The simplest refracting telescope contains only the objective lens and the eyepiece; however, they can come in many different configurations.
One problem with refracting telescopes is that images may not appear sharply defined. This is known as an aberration or distortion. In refracting telescopes, the major distortion is known as chromatic aberration, due to light of different colors being refracted differently. This means that blue light and red light will not have the same focus.
Reflecting telescopes use mirrors to gather and focus light. A primary mirror reflects light back to a focus. The primary mirror is usually concave or parabolic, as shown in the diagram. A small mirror then reflects the light into the eyepiece.
The first reflecting telescope was designed by English mathematician and physicist Isaac Newton as an alternative to refracting telescopes which suffered from severe chromatic aberration. However, reflecting telescopes still suffer from distortions, particularly spherical aberration. Light rays at different points on the curve of the mirror are reflected along different paths. This means that the rays do not focus at a single point.
A catadioptric telescope is one which combines the best features of both refracting and reflecting telescopes. This means that they use both lenses and mirrors to create an image. This type of telescope generally has a spherical primary mirror, a thin correcting lens and an eyepiece. This lens corrects any spherical aberration while adding minimal chromatic aberration. This results in a relative aberration-free field of view.
Catadioptric telescopes have been widely used in astronomy. The largest telescope of this type is the James Gregory telescope which is used for the study of black holes.
A telescope is a device which collects and focuses electromagnetic radiation to create a magnified image. Optical telescopes are telescopes for visible light. There are three primary types of optical telescope. These are refracting, reflecting and catadioptric telescopes. Refracting telescopes use lenses to produce an image, reflecting telescopes use mirrors and catadioptric telescopes use a combination of the two. Refracting telescopes suffer from chromatic aberration where light of different colors is focused differently. Reflecting telescopes, which use non-parabolic mirrors, suffer from spherical aberration. Catadioptric telescopes were designed to reduce the impact of these aberrations.
The first telescopes were refracting telescopes. The technology for producing good quality lenses, introduced after the 13th century, allowed this type of telescope to be built. Galileo improved the design and was able to use his telescope to make astronomical observations for the first time.
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Telescopes are used to make distant objects appear larger. They magnify distant objects with mirrors, lenses or a combination of the two.
The first telescopes were used to watch for incoming ships. Merchants wanted to be the first to see incoming ships so that they could sell their products first.
The telescope is important because it has a wide variety of uses. Telescopes can be used in areas such as astronomy, aviation, navigation and in military applications.
An optical telescope is used to help see distant objects easily. They gather and focus visible light to create magnified images of objects.
A telescope uses mirrors or lenses to reflect or refract light to a single point, called the focal point, forming an image. An eyepiece is then used to view the image. They can be used to make very far away objects appear larger.
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