Telescopes

A telescope is an instrument specifically designed to view remote objects through use of electromagnetic radiation. The most common type of telescope is the optical telescope, which operates through gathering and focusing light from the visible part of the electromagnetic spectrum. Some telescopes work in infrared light or in ultraviolet. Optical telescopes enhance the brightness of distant objects and the angular size.

Electromagnetic Spectrum The electromagnetic spectrum is the range of every possible frequency in electromagnetic radiation. The electromagnetic spectrum of an object is determined by the certain distribution of radiation both emitted and absorbed by the object.

How it Works So that the optical telescope can receive, observe, photograph, study and send images to a computer, it employs a variety of optical elements such as glass – lenses or mirrors to gather light and other electromagnetic radiation to bring the said light and radiation to a focal point.

The basic light gathering element, the objective (the convex lens or concave mirror used to gather incoming light) focuses that light from the distant object to a focal plane where it forms a real image. This image can then be recorded or viewed through an eyepiece, which acts like a magnifying glass. We then see an inverted, magnified virtual version of the real object.

Inverted Images Most telescopes use a system of inverted images, produced at the focal plane. These are called inverting telescopes. In astronomical telescopes the inverted view usually stays uncorrected for it doesn’t affect the way the telescope is used.

Real and Virtual Images A virtual image is created when the outgoing beams of light from a point on the object do not actually intersect, or meet, at a point. An example of this is looking at yourself in front of a flat mirror and perceiving the image to be at a doubled distance away from you. If you look into a mirror and are standing a metre from the mirror, your reflection will appear to be two metres away. A real image, on the contrary, is a representation of the object, in which the perceived location of the object is a meeting of the rays of light that make up the image. An example is of the images seen on a cinema screen. The source is the projector and together with the rear camera detector produces an image, which is then produced on the human retina.

Types of Telescopes Telescopes are often used in astronomy. There are three main types:

The Refracting Telescope It uses lenses to form an image. The refracting telescope uses an objective lens and a type of eyepiece together to collect more light than the human eye could gather unaided. It focuses the light onto a focal plane and gives the viewer a clearer, brighter and larger picture of the object, a magnified virtual image.

The Reflecting Telescope It uses a collection of mirrors to form the image. Light bounces off a large concave mirror, which in turn focuses the light on a secondary mirror. The most common type of focus is Coude’s focus. This method uses two extra mirrors to reflect the image outside of the telescope, so that the image can be seen through a lens or photographed.

The Catadioptric Telescope This uses both a combination of lenses and mirrors to form an image; the lens might be in front of the mirror or somewhere along the optical path to create the image. If used in a prime focus configuration they can have a very wide coma free field of view.

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