Light and Lenses Chapter I PDF

Light and Lenses 1. Course Description This course is designed to help the students acquire knowledge necessary for understanding characteristics of unifocal and multifocal lens reference points as a basis for physical and geometical optics List of Topics Contact Hours 1 In...

Light and Lenses 1. Course Description This course is designed to help the students acquire knowledge necessary for understanding characteristics of unifocal and multifocal lens reference points as a basis for physical and geometical optics List of Topics Contact Hours 1 Introduction to Ophthalmic Optics 3 2 Refraction , Reflection and Prism 3 4 Refractive Power and Lenses 3 5 Sphero- Cylindrical Lenses 3 7 ‫التحميل‬ Lens Form and Thickness ‫…يجري‬ 6 The Eye and Refractive Errors 3 3 3 8 Aberrations and Lens Design 3 9 Ophthalmic Prisms 6 Assessment Tasks for Students Percentage of Total Assessment task Week Due Assessment Score 1 1st Quiz 4 10% 2 Midterm exam 7 20% 3 2nd Quiz 9 10% 4 presentation 10 10% 5 Homework Every 3W 10% 6 2-hour written exam 12 40% Reflection Occurs, at some degree, at all interfaces even when most of the light is transmitted or absorbed. Laws: ‫…يجري التحميل‬ – The Incident ray, the Reflected ray & the Normal.. All lie in the same plane. – Angle of Incidence = Angle of Reflection Reflection at spherical mirrors concave convex concave convex Light Refraction It’s the change in direction of light when it passes from one transparent medium into another of different optical density. The higher the density, the slower light and the higher the refractive index.  ‫‪Lenses‬‬ ‫…يجري التحميل‬ What is a lens? A lens is a transmissive device that disperses or focuses light beams by refraction. Basic Types of Lenses Convex Concave What is the main difference between a lens and a mirror? The main difference between a lens and a mirror is that light rays are refracted through a lens while mirrors reflect or bounce back light rays. Type of Image mirrors produce images by reflection, lenses produce images by refraction. Depending upon their “thickness”, lenses are classified as “thick” or “thin”. In this course, we will only consider “thin” lenses. In effect, therefore, we disregard the thickness of the lens assuming it to be a line. Type of Image Real or Virtual Enlarged or Reduced Erect or Inverted # When representing “thin” lenses in a diagram, it is sometimes more convenient to simply draw an arrow rather than the actual lens. Using this method, an arrow is used to represent the lens as illustrated below. - Ray Diagram for Convex Lens Rules for Ray Diagrams for Convex Lens 1. A parallel ray refracts through the focal point. 2. A ray through the center of the lens continues straight. 3. A ray coming through the focal point, refracts parallel to the principal axis. The characteristics of the image formed by a converging lens depend upon the location of the object. There are six "strategic" locations where an object may be placed. For each location, the image will be formed at a different place and with different characteristics. We will illustrate the six different locations and label them as Case-1: Object at infinity Case-2: Object just beyond 2 F’ Case-3: Object at 2F’ Case-4: Object between 2F’ and F’ Case-5: Object at F’ Case-6: Object within focal length (f) XV I =01/1 +ist 27sF - 45 Es Nisf - & - & * S - C &  ‫‪is‬‬ ‫‪ind‬‬ ‫‪-‬‬ ‫‪-‬‬ ‫…يجري التحميل‬  Summary for Convex Lens When the object is: Then the image is: –Beyond 2F –Between 2F and F –At 2F –At 2F –Between 2F and F –Beyond 2F –At F –No image –Between F and lens –Virtual image What is the Power of a Lens? The ability of a lens to bend the light falling on it is called the power of a lens measurement by dioptre. Since the lens of shorter focal length will bend the light rays, more will have more power. A convex lens converges the light rays towards the principal axis whereas a concave lens diverges the light rays away from the principal axis. The inverse of the focal length in meters, or D =1/ f, where D is the power in dioptres. Unit is dioptre (D) The power of a lens is specified as the inverse of the focal length in meters, or D =1/ f, where D is the power in dioptres. F = 1 / 0.25 = 4.00 D F = 1/ 0.10 = 10.00 D  lens-maker’s equation Lens Formed by two curved boundaries between transparent media. Lenses often have spherical surfaces. The curved surfaces are parts of large spheres of radius R1 or R2. - n = 1.5