Six Chapter 11

Some Applications of Lenses

• Used in projectors

• The condenser ensures uniform illumination of the slide or movie.
• The converging mirror and light illuminate the slide or movie
• The slide is placed between one and two focal lengths from the projector lens so that a large real image is produced.
• The image is upside down; therefore, the slide or movie film must be placed in the projector upside down.
• The projection lens is in a tube so it can be moved back and forth to focus the image.
• Used in microscopes
• The simple microscope is just a magnifying glass with the object placed inside the focus. This produces a virtual image.

• The compound microscope uses two lenses arranged as in the diagram below.

• The objective produces an enlarged inverted real image
• The image is inside the focus of the eyepiece and acts as the object for the eyepiece.
• The eyepiece then produces an enlarged erect virtual image.
• Focus is achieved by mounting the eyepiece in a tube that can be moved back and forth.
• Used in telescopes

• Astronomical telescopes – has two converging lenses
  • Light from a distant object is nearly parallel and forms a real inverted image near the focal point of the objective.
  • This image is just inside the principal focus of the eyepiece.
  • The eyepiece acts like a magnifying glass producing an inverted virtual large image.
• Terrestrial telescopes – have a third lens between the objective and eyepiece.
  • The purpose of the third lens is to make an erect image.
• Prism binoculars – consists of two refracting telescopes mounted side by side.
  • Between the objective and the eyepiece is a pair of prisms. These invert the image to make it erect.
  • The prisms also reduce the distance between the two lenses and make the device smaller

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November 21, 2013