Optometric optics

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Optometric optics

  1. 1. OPTOMETRIC OPTICS BY Dr.S.PALANISWAMY
  2. 2. 2- Nomenclature (naming System)1- A ray it is an imaginary line extending from the focus to the wave-front. It represents the direction of propagation of the wave-front.2- A pencil of light it is a bundle of rays emanating from a point source after passing through a limiting aperture ( pinhole effect)3- A beam of light it is a collection of pencils arising from an extended (infinite-sized) source, or from a source of finite size
  3. 3. Nomenclature Continues4- Object it is a physical source of light, or no light, existing in object space and it is divided to a) real object is from which the light rays diverge or are reflected from b) Virtual object is one towards which light is converging before interruption by the surface of an optical system5- Image It is the projection of an object in image space. It is formed by light traveling from an object, in image space, after an optical system has acted on the light it is divided to two different types; Real image and virtual image.
  4. 4. Nomenclature Continues6- Real image It is formed by the actual convergence of rays reflected or refracted by an optical system. A real image can by caught on a screen it the screen placed in the image space ( the focus).7- Virtual Image it is formed by the light divergence from point in the optical system. The virtual image can’t caught on the real screen until it changed to a real image.8- Object space it is related to all the space in which light has traveled before being interrupted by the optical system.9- Image Space This is the space within which light travels after being acted upon by an optical system.The Primary (object) applies to points in object space.The secondary (Object) applies to point in image space.
  5. 5. Theories of light1. Wave theory: light behaves like a wavea) frequency, speed, and wavelength2. Particle theory: light behaves like a particlea) Discrete "packet" of energy is a photon.3. Neither is perfect; both are used depending on the subject4. Geometric optics:a) Most of what we cover in these notesb) Light is a "ray" - an artificial construct
  6. 6. Reflection
  7. 7. Reflection• We know that white light has seven colors namely violet,indigo,blue,green,yellow,orange and red. When ever light falls on an object, all the colors, except the color of that object, are absorbed by that object and the color corresponding to that object is reflected. When this falls on our eyes we can see the color of that object. This whole process uses the phenomenon of reflection of light. For example consider a leaf it has green colored chlormphyll pigment , it absorbs all colors present in white light except green color, and green light is reflected, this light ray when touches our retina makes us sense that leaf is in green color.
  8. 8. Refraction
  9. 9. Refraction of Light• Refraction is the bending of a wave when it enters a medium where its speed is different. The refraction of light when it passes from a fast medium to a slow medium bends the light ray toward the normal to the boundary between the two media. The amount of bending depends on the indices of refraction of the two media and is described quantitatively by Snells Law.• As the speed of light is reduced in the slower medium, the wavelength is shortened proportionately. The frequency is unchanged; it is a characteristic of the source of the light and unaffected by medium changes.
  10. 10. Absorption of Light
  11. 11. Absorption of Light• The absorption of light in the simplest case starts with a beam of light of intensity I of photons that has just penetrated into a material with a uniform concentration of absorbing pigments.• The mechanism for absorption is that a photon transfers all its energy to an electron in the absorbing material.• The photon is "lost" from the light beam as it is absorbed in a single event. The electron is excited by the gain in energy to a higher energy state in the electron configuration around the atom.
  12. 12. Refraction through Prism
  13. 13. Refraction through PrismThe σ is the angle of the Prism and the δ isthe angle of deviation.
  14. 14. Sign Convention• The sign convention rule that used in the optics field will be1- incident light will be consider as traveling from left to right - +2- all distance that measured in the optical system concerned the following a) if it is measured in the same direction of the incident light will be Positive + b) it is measured in the opposite direction of the incident light , it will be consider as negative -3- Vertical distance above the optical axis is positive and the one below is negative4- The angle between the ray and the optical axis is measured from the ray to the optical axis5- Angles of incidence, reflection, and refraction are measured from the normal to the ray6- angle measured in the counterclockwise is positive and the one in clockwise is negative7- An arrowhead on a line or curve fixing the limit of the distance or angle being measured indicates the direction in which that distance or angle is being measured8- Vergence is the spread of light rays at a specific distance from the focal point9- light moving towards the focus is consider as a converging ( +)10 – Light moving away from the focus is consider as a diverging (-)11- the measuring unit of vergence is the Diopter. The vergence of a particular ray system is the reciprocal of the distance from the wave-front to the center of curvature (focus), in meter
  15. 15. Fresnel prism• For patients suffering from double vision due to a variety of conditions, one possible correction is to tilt all the light that comes into one eye. Then the image coming into one eye is shifted to line up with the unshifted image in the other eye. A glass wedge or prism does exactly that kind of shifting. It’s impractical to put a glass wedge in front of one eye, but there’s another type of prism called a Fresnel prism that does the same job in a thin sheet of plastic. This Fresnel prism film is designed to be adhered directly to the lens of a pair of eyeglasses.
  16. 16. Instructions• Remove the lens from the frame.• Align the prism film correctly, lay it on the lens, and cut the film to match the lens outline. The ridged side will point towards the wearer’s eye, while the smooth side will adhere to the inside surface of the lens.• Trim the edges of the prism to fit inside the beveled edge of the lens. Slide the razor blade against the bevel of the lens, at the angle of the bevel, so that the film is trimmed inside the beveled edge.• Clean the lens and the prism in warm soapy water. Rinse.
  17. 17. Instructions Continued• Submerge the lens and prism in a bucket or tub of clean water. Brush any bubbles off the surfaces to be mated. Place the bottom edges together and press the prism onto the lens in a kind of rolling motion, as if laying a pie crust on a cutting board.• Remove the lens assembly from the water and push any bubbles out by gently pushing on the prism film with your thumb, shepherding the bubbles out. Slide the prism to position it properly, if necessary.• Replace the lens in the frame. Be careful not to catch any of the Fresnel prism film between the lens and frame.

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