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Lenses

Lenses. Night Vision. Night Vision. Night vision goggles use lenses to focus light onto a device called an image intensifier. Inside the intensifier, the light energy releases a stream of particles. These particles then hit a phosphor-coated screen.

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Lenses

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  1. Lenses

  2. Night Vision

  3. Night Vision • Night vision goggles use lenses to focus light onto a device called an image intensifier. • Inside the intensifier, the light energy releases a stream of particles. • These particles then hit a phosphor-coated screen. • The phosphors glow when the particles strike them. • The person wearing the goggles sees a glowing green image

  4. Lens • A lens is a curved transparent material that is smooth and regularly shaped so that when light strikes it, the light refracts in a predictable and useful way.

  5. Most lenses are made of transparent glass or very hard plastic. • These materials have several useful properties. • For example, they are strong and hard. • They can also be shaped and polished. • By shaping both sides of the lens, it is possible to make light rays diverge or converge as they pass through the lens.

  6. The most important aspect of lenses is that the light rays that refract through them can be used to magnify images or to project images onto a screen. • Relative to the object, the image produced by a thin lens can be real or virtual, inverted or upright, larger or smaller.

  7. Converging Lens • Lens that is thickest in the middle • Parallel light rays converge through a single point after refraction

  8. Converging Lens • A converging lens can be used as a magnifying glass.

  9. Diverging Lens • Lens that is thinnest in the middle • Parallel light rays spread apart after refraction

  10. Diverging Lens • A diverging lens forms an upright, smaller image.

  11. Terminology • Principal axis • The axis of symmetry is a vertical line drawn through the optical centre. • Both kinds of lenses have two principal focuses.

  12. Terminology • The focal point where the light either comes to a focus or appears to diverge from a focus is given the symbol F, while that on the opposite side of the lens is represented by F’. • The focal length, f, is the distance from the axis of symmetry to the principal focus measured along the principal axis.

  13. Emergent Ray • The light ray that leaves a lens after refraction Emergent Rays

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