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Hubble Space Telescope (HST) Hubble Space Telescope (HST): A pioneer of invention After 400–year progression from Galileo's first primitive hand held astronomical telescope, today we have huge telescopes, of which the Hubble Space Telescope (HST) is undoubtedly the most famous. These modern telescopes have many remarkable qualities that enormously extend our natural ability to view the Universe. They gather much more light than our eyes – a million times more in the case of HST. They make objects look much bigger, as if the object were much closer – up to 50,000 times closer, a HST can read a wristwatch from a distance of 10 miles. Lets learn more about these latest optical instruments.

Learning objectives

After completing the topic, the student will be able to:

  • Observe and explore optical instruments that are available in daily life.
  • Investigate the characteristics of human eye and probe the reasons for the cause of vision defects.
  • Distinguish between simple and compound microscope based on their characteristics of magnifying a given object.
  • Explore how we can image a cosmic object using a telescope and discuss various types of telescopes.
  • Explore the concept of holography and its applications in everyday science based on its characteristics.
  • Discover the working of binoculars, cameras, periscopes based on simple principles of refraction and reflection.
IRIS TELESCOPE IRIS telescope This instrument is a combination of an ultraviolet telescope and a spectrograph. The telescope provides high-resolution images, while capturing data on about 1% of the sun at a time. The images can resolve very fine features, as small as 150 miles across.
Optical instruments

Optical instruments process light waves to enhance an image for viewing or analyzing light waves to determine its characteristic properties. The very first optical instruments were telescopes and microscopes used for magnifications of images. Mirrors and lenses find their applications in very many walks of life. Since the days of Galileo, these optical instruments have been greatly improved and extended into other portions of the electromagnetic spectrum. These instruments employ calculations of positions of objects and images from ray diagrams that we have discussed in "Spherical Mirrors and Lenses".

Some optical instruments that we come across are:

  • The human eye – convex lens.
  • Corrections of defects of vision – combinations of concave and convex lenses.
  • Compound microscope – double convex lens.
  • Telescope – convex lenses.
  • Holography – combination of convex lens and mirrors.
  • Three dimensional viewers – combination of convex lenses.
  • Binoculars – prisms, convex lenses and mirrors.
  • Camera – combination of convex lenses.
  • Periscope – plane mirrors or prisms.
The human eye Cross-sectional view of the human eye The image formed inside the human eye is inverted. But the information sent to the brain would be corrected. Hence an eye can see things as they really are.

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Human eye

The most remarkable optical instrument known is the eye. Light enters the eye through the transparent cover called the cornea, which does about 70% of the necessary bending of the light before the light passes through the pupil (which is an aperture in the iris). The light then passes through the lens, which is used only to provide the extra bending power needed to focus images of nearby objects on the layer at the back of the eye, the retina.

The lens is held by ciliary muscles, which stretch and relax to change the focal length of the lens. The distance of the image that a lens produces on the retina depends on the object distance and the focal length of the lens. In the case of the eye lens, however, the image is always produced on the retina no matter where the object is. In other words, for the eye lens, the image distance is fixed. Therefore the focal length of the eye lens must change in accordance with the object distance. This is the function of ciliary muscles.