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Chapter 12 Lenses and lens technologies

12.1 Characteristics of Lenses. Chapter 12 Lenses and lens technologies. Today we will learn about ... the different types of lenses, the characteristics of the image formed by each of those lenses, and some of the practical difficulties in making those types of lenses.

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Chapter 12 Lenses and lens technologies

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  1. 12.1 Characteristics of Lenses Chapter 12Lenses and lens technologies

  2. Today we will learn about ... • the different types of lenses, the characteristics of the image formed by each of those lenses, and some of the practical difficulties in making those types of lenses. • aberration, which occurs when the rays of light do not completely focus at the same point, and the reasons different types of aberration exist. Learning Goals

  3. A lens is a transparent object with at least one curved side that causes light to refract. 12.1 Characteristics of lenses • Reading stones made from transparent pieces of quartz or glasswere the earliest type of lens used to magnify written text.

  4. Modern lenses come in many sizes and have a variety of uses. 12.1 Characteristics of lenses

  5. The terms plane (or plano), concave, and convex are used to describe the shape of lenses as well as mirrors. Unlike mirrors, lenses have two sides, either of which can be plane, concave, or convex in shape. Describing lenses

  6. The combination of shapes that are present in a lens determines whether the lens causes parallel light rays to diverge (spread out) or converge (come together) and by how much. Describing lenses

  7. A window pane causes light rays to shift to the side (lateral displacement) but not change their direction relative to each other. Describing lenses

  8. A converging lens brings parallel light rays toward a common point. A lens that is convex on both sides (biconvex or double convex) best illustrates convergent behaviour. Describing lenses: Converging lenses

  9. The convergence is caused by rays first refracting toward the normal when light enters the glass and then refracting away from the normal when they leave. Describing lenses: Converging lenses

  10. A diverging lens spreads parallel light rays away from a common point. A lens that is concave on both sides (biconcave or double concave) best illustrates divergent behaviour. Describing lenses: Diverging lenses

  11. The principal axis of a lens is a straight line that passes through the centre of the lens, normal to both surfaces (sides) of the lens. Focal point & focal length of lenses • When rays that are parallel to the principal axis pass through a converging lens, the rays intersect at a point called the focal point (F).

  12. The distance from the focal point to the centre of the lens is called the focal length (f). Focal point & focal length of lenses

  13. To find the focal point (F) for a diverging lens you must extend the rays behind the lens, finding the virtual focus (virtual focal point). Focal point & focal length of lenses • As with the converging lens, the focal length (f) is the distance between the centre of the lens and F.

  14. The position of the focal point for a lens depends on both the index of refraction of the lens material and the curvature of the lens. Focal point & focal length of lenses

  15. A larger curvature in either a converging or a diverging lens results in more bending. Focal point & focal length of lenses

  16. For thick lenses, only light rays that pass through the lens near the principal axis meet at the focal point and give a sharp image. Thick and thin lenses

  17. Thick and thin lenses • A fish-eye lens drastically distorts the image , but it brings a much largerarea into view. It is an example of spherical aberration.

  18. Chromatic aberration is the dispersion of light through a lens. The edges of lenses act as prisms, splitting light into colours. Thick and thin lenses: Chromatic Aberration Chromatic aberration is most visible along the edges of objects. As a result of dispersion, different colours of light are focused at different points.

  19. Spherical and chromatic aberration can be partially corrected by combining one or more lenses, especially if the lenses are made of materials with different indices of refraction. Correcting Chromatic Aberration

  20. Strategies that can be used to reduce chromatic aberration include: using two thinner lenses instead of one thick one; combining lenses made of different materials; or combining many lenses. Correcting Chromatic Aberration Two separate lenses that are thinner than a single lens can reduce spherical aberration. A combination of lenses made of different types of glass can reduce chromatic aberration.

  21. HOMEWORK • From textbook: • Page 489 # 1-4 • Page 493 # 3-8

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