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Introduction to optics

Introduction to optics. Dr. Soujanya K MBBS, MS, DNB, FPRS Assistant Professor, Dept Of Ophthalmology, YMCH. What is light?. V I B G Y O R. Jab we met : Light meets an object??. Reflection. Absorption. Transmission. What is refraction?. “REFRACTION”. Emergent ray. Refracted ray.

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Introduction to optics

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  1. Introduction to optics Dr. Soujanya K MBBS, MS, DNB, FPRS Assistant Professor, Dept Of Ophthalmology, YMCH

  2. What is light?

  3. VIBGYOR

  4. Jab we met : Light meets an object??

  5. Reflection Absorption Transmission

  6. What is refraction?

  7. “REFRACTION” Emergent ray Refracted ray Incident ray

  8. Light passing from one transparent medium to another of different optical density changes its speed. This results in a change in its direction of movement as soon as it enters the second medium.

  9. Prism

  10. Lenses Lens

  11. Cardinal data of a lens • Centre of curvature (C) • Radius of curvature (r) • The principal axis (AB) • Optical centre (O) C O r C A B

  12. The principal focus (F) • The focal length (f) • Power of a lens (P) O F f

  13. Types of spherical lenses • Convex • Concave

  14. Convex Lenses The magnifier Object seen through it moves in the opposite direction to the lens

  15. Concave Lenses object seen through it moves in the same direction as the lens.

  16. Cylindrical lens • Acts only in one axis i.e., power is incorporated in one axis, the other axis having zero power. • A cylindrical lens may be convex (plus) or concave (minus)

  17. Cylindrical lens has a power only in the direction at right angle to the axis. • Parallel rays of light after passing through a cylindrical lens do not come to a point focus but form a focal line

  18. TORIC SURFACE / ASTIGMATIC SURFACE ORANGE EGG

  19. Sturm's conoid • The configuration of rays refracted through a toric surface is called the Sturm’s conoid.

  20. The more curved meridian will have a greater refractive power than the less curved; hence if parallel rays fall upon a convex astigmatic surface the vertical rays will come to a focus sooner than the horizontal.

  21. FOCAL INTERVAL OF STURM

  22. At the dioptric mid-point between these two focal lines, the astigmatic focus forms a circular patch known as the circle of least confusion circle of least confusion

  23. Refractive components of the eye 1. The cornea which is the major refracting surface (about + 40 D). 2. The aqueous humour. 3. The lens (about + 20 D). 4. The vitreous body. NB. The total diopteric power of the eye is about + 58 D.

  24. Refracting medium Refractive index Air 1.000 Cornea 1.376 Aqueous humour 1.336 Lens (cortex-core) 1.386-1.406 Vitreous humour 1.336

  25. Eye is a bunch of lenses. MAJOR REFRACTIVE INTERFACES

  26. Gullstrand's concept of a schematic eye. • three pairs of cardinal points, which are situated on the principal axis of the system.

  27. F1 F2 P1 P2 N1 N2 1.35 1.60 7.08 7.33 24.4 15.7 TOTAL DIOPTRIC POWER OF EYE(+58D) = CORNEA (+43D) + LENS (+15D) 1 F1,2 Principal foci 2 Principal points P1 P2 Nodal points 3 N1 N2

  28. Listing's reduced eye. • Listing has simplified the optical data • Single Principal point • Single Nodal point

  29. F1 P F2 N 1.5 7.2 24.4 15.7 TOTAL DIOPTRIC POWER OF EYE :+60D

  30. OPTICAL ABERRATIONS • Imperfections or lapses in the optical system • They normally exist to a small degree but functionally they are usually immaterial. • These include: • 1. Diffraction of light. • 2. Spherical aberrations. • 3. Chromatic aberrations. • 4.Coma etc

  31. Bending of light caused by Edge of an aperture or Rim of a lens Diffraction of light

  32. The actual pattern of a diffracted image point produced by the pupil is a series of concentric dark and bright rings. At its centre is a bright spot known as the Airy Disc. Diffraction blur increases with the small size of the pupil Diffraction of light

  33. Spherical lens refracts peripheral rays more strongly than paraxial rays As a result the incoming rays do not come to a point focus Spherical aberrations

  34. Occurs due to to the fact that the RI of any transparent medium varies with the wavelength of the incident light. Blue light is focussed slightly in front of the red Chromatic aberrations

  35. Emmetropic eye-hypermetropic for red and myopic for blue & green. This forms the basis of the duochrome test in subjective refraction. Chromatic aberrations

  36. coma • Light rays entering the optical at an angle are focused at different points than those entering the optical system on or near the optical axis. • Results in a comet-like image being formed away from the middle of the image

  37. Summary • What is light? • Refraction • Types of lenses • Sturmsconoid • Schematic eye • Reduced eye • Optical aberrations

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