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# geometrical Optics

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### geometrical Optics

1. 1. OBJECTIVES:1. Discuss principles of pinhole imaging, mirror and lenses.2. Define object and image characteristics3. Discuss principles of light propagation
2. 2. GEOMETRICAL OPTICS Deals primarily with imagingPHYSICAL OPTICS Wave nature of lightQUANTUM OPTICS Particle nature of light and interaction of light and matter
3. 3. DEFINITION OF TERMS CONJUGATE- correspondence between object and image points RAY- the route that light follows as it travels from an object point to the image point PENCIL of light- small bundle of rays that travel in the same direction
4. 4. PINHOLE IMAGING
5. 5. OBJECT CHARACTERISTICS REAL objects ◦ Can be felt, touched, located in front of the optical system VIRTUAL objects ◦ Cannot be felt or touched, located behind an imaging system LUMINOUS ◦ Objects that produces its own light (eg. candle)
6. 6. IMAGE CHARACTERISTICSMAGNIFICATION Most important enlargement Making images smaller or larger than the object ◦ Transverse = image height/ object height ◦ Axial ◦ angular
7. 7. 4 cmObjectHeight Image 2 cm height Transverse magnification = 2/4 = -0.5
8. 8.  AXIAL MAGNIFICATION ◦ Aka longitudinal magnification ◦ Axial magnification = ( transverse magnification) 2 ANGULAR MAGNIFICATION ◦ The ratio of the angle subtended by an object without the lens or magnifier
9. 9. IMAGE LOCATION The distance between a reference point and the image Reference point- back surface of the lens Positive- image is right to the reference point
10. 10. DEPTH OF FOCUS Image appears sharp within this region
11. 11. DEPTH OF FIELD
12. 12. Object w/n thisregion appear sharp in the DEPTH OF FIELD image
13. 13. IMAGE QUALITY Images are imperfect facsimiles. Each object point produces a 2- mm diameter spot in the image= BLUR circles STIGMATIC IMAGE- a perfect point image of an object point The smaller the blur circle- less image details lost
14. 14. BRIGHTNESS and IRRADIANCE BRIGHTNESS- A visual perception The response of the nervous system to light entering the eye IRRADIANCE A purely physical measure of the amount of light per unit of an image Important in calibration of perimeter
15. 15. Wavelength570 nm
16. 16. LIGHT PROPAGATION
17. 17. OPTICAL MEDIA ANDREFRACTIVE INDEX Medium- any material that transmits light Light travels at different speeds in different media REFRACTIVE INDEX- N= speed of light in vacuum speed of light in medium ◦ is always greater or equal to 1
18. 18. REFRACTIVE INDEX FOR SOME MATERIALS OF CLINICAL INTERESTMATERIALS REFRACTIVE INDEXAIR 1.0000WATER 1.3333CORNEA 1.376AQUEOUS/VITREOUS 1.336SPECTACLE CROWN 1.523GLASSPMMA 1.492
19. 19.  Dispersion- short wavelengths travel slowly than long wavelengths Leads to chromatic abberation Eye- 0.5 D of chromatic abberation
20. 20. RED BLUEBLUE REDRED BLUE
21. 21. LAW OF RECTILINEARPROPAGATION Light in a single medium travels along straight- line paths called rays Pencil of light- a bundle of rays traveling close to each other in the same direction
22. 22. OPTICAL INTERFACE The boundary separating 2 different optical media Smooth- light undergo specular reflection and transmssion Rough- diffuse reflection and transmission
23. 23. Smooth optical interface
24. 24. SPECULAR REFLECTION: LAW OF REFLECTION The direction of the reflected ray bears a definite relationship to the direction of the incident ray Reflected ray lies in the same plane as the incident ray and the surface normal and that θ i = θr
25. 25. Smooth optical interfaceθi θr
26. 26.  Reflection coefficient Used to calculate the amount of light transmitted at an optical surface R= n2-n1 2 n2+n1
27. 27. How much more reflective is an acrylic IOL than a siliconeIOL? Assume that the index of refraction of acrylic is 1.55 andthe silicone is 1.43. ( aqueous= 1.33) R acrylic = 1.55-1.33 2 1.55+1.33 0.0584 =0.584% R silicone= 1.43 - 1.33 2 1.43 + 1.33 0.00131= 0.131%  0.584/0.131= 4.46
28. 28. SPECULAR TRANSMISSION: Lawof Refraction The transmitted ray’s direction bears a definite relation to the incident’s ray direction Snell’s law= the refracted or transmitted ray lies in the same plane as the incident ray and the surface normal Light- lower- higher refractive index– bends toward the surface normal
29. 29. N1<n2 optical interface N1>n2Incident ray θi θi θ Surface normal θt
30. 30. TOTAL INTERNAL REFLECTION Occurs when light travels from a high- index medium to a low –index medium and the angle of incidence exceeds a certain critical angle Critical angle- angle of incidence that produces a transmitted ray 90° to the surface normal
31. 31. DISPERSIONRefractive indices are not fixed values Refractive indices- wavelengths
32. 32. Fermat’s principle Light travels from one point to another along the path requiring the least time Optical path length- distance light travels in a given medium multiplied by the medium’s refractive index e.g Light travels 5 cm in air (n= 1.000) and 10 cm in glass ( n= 1.523) OPL= 5 cm x 1.000+ 10 cmx 1.523= 20.2 cm
33. 33. BA air glass
34. 34. Path 1O I Path 2
35. 35. “I have been a multitude of shapes, Before I assumed a consistent form”-Taliesin