principals of optical and engineering .ppt
- 1. 1 1 Lecture 4 Lecture 4th th objectives: objectives: Identify the physical Identify the physical principals of optics. principals of optics. Outline the retinal Outline the retinal images images.
- 2. 2 2 1 1st st Lecture objective: Lecture objective: Identify the Identify the physical physical principals of principals of optics. optics.
- 3. 3 3 Physical Principals of Optics: Physical Principals of Optics: Light Light is a form of is a form of electromagnetic electromagnetic radiation radiation composed of packets of energy called composed of packets of energy called photons photons that travel in that travel in wavelike wavelike fashion fashion. . The The forward forward movement movement of a light wave in a of a light wave in a particular direction is known as particular direction is known as light light rays rays. . The The wavelength wavelength is the is the distance distance between between 2 2 successive successive wave wave peaks peaks The eye The eye photoreceptors photoreceptors are are sensitive sensitive to to wavelength between wavelength between 400 400 – – 700 700 nanometers nanometers which is called the which is called the visible zone visible zone. . There are 2 There are 2 invisible zones invisible zones; ; ultraviolet ultraviolet & & infrared infrared rays rays. .
- 4. 4 4 Properties of an electromagnetic wave Properties of an electromagnetic wave
- 6. 6 6 Lights of different wave lengths is Lights of different wave lengths is perceived as different colour perceived as different colour sensations. sensations. Short Short wave wave lengths are sensed as lengths are sensed as VOILET VOILET & & BLUE BLUE. . long long wave wave lengths are interpreted as lengths are interpreted as ORANGE ORANGE & & RED RED. . The The intensity intensity of of light light is the amplitude is the amplitude or or height height of the wave. of the wave.
- 7. 7 7 Sensitivity of the three types of cones to Sensitivity of the three types of cones to different wavelength different wavelength
- 8. 8 8 Refraction Refraction of light ray: is the of light ray: is the bending bending of light of light rays which occurs when the ray passes from a rays which occurs when the ray passes from a medium of medium of one one density density → a medium of a → a medium of a different different density density. . Lights waves Lights waves travel travel through through AIR AIR at a velocity of at a velocity of about about 300000 300000 km/second km/second but much but much slower slower through transparent media such as through transparent media such as water water & & glass glass. . Refractive Refractive index index of transparent substance of transparent substance velocity velocity of light rays in of light rays in air air = --------------------------------------------- = --------------------------------------------- velocity velocity of light rays in this of light rays in this substance substance So the refractive index of air is ONE. So the refractive index of air is ONE.
- 9. 9 9 Focusing of diverging light rays by human eye Focusing of diverging light rays by human eye
- 10. 10 10 Application of refractive principles to lenses: Application of refractive principles to lenses: Convex Convex lens lens → → converges converges parallel rays → parallel rays → focal focal point. point. Concave Concave lens lens → → diverges diverges parallel rays → parallel rays → wide wide area. area. Nodal Nodal point point = = central central part of the lens. part of the lens. Focal Focal length length ( (F F) = is the ) = is the distance distance between the between the nodal nodal point & the point & the focal focal point. point. The lenses unit The lenses unit power power is is DIOPTER DIOPTER. . 1 1 The power of certain lens in diopter = --------- The power of certain lens in diopter = --------- F F i.e. power of a lens having a focal length 1 meter = i.e. power of a lens having a focal length 1 meter = 1/1 = one diopter & that having a focal length 2 1/1 = one diopter & that having a focal length 2 meter = 1/2 = 1/ 2 diopter meter = 1/2 = 1/ 2 diopter
- 11. 11 11 Refraction by convex & concave lenses Refraction by convex & concave lenses
- 12. 12 12 2 2nd nd Lecture objective: Lecture objective: Outline the Outline the retinal images retinal images.
- 13. 13 13 Retinal images: Retinal images: Lens system of human eye can focus an Lens system of human eye can focus an image on the retina. image on the retina. The image is The image is INVERTED INVERTED & & REVERSED REVERSED with with respect to the object. respect to the object. This This position position is is correct correct by the by the visual visual cortex cortex. . Size of object (1) Size of object (1) distance of object from lens distance of object from lens nodal point (2) nodal point (2) ------------------------ = ---------------------------------- ------------------------ = ---------------------------------- Size of image (3) Size of image (3) distance of image from lens distance of image from lens nodal point (4) nodal point (4) If we know no. 1, 2 & 4 we can calculate no. 3. If we know no. 1, 2 & 4 we can calculate no. 3.
- 14. 14 14 Inversion of the image on the retina Inversion of the image on the retina
- 15. 15 15 Optic axis is a straight line that joins the Optic axis is a straight line that joins the anterior & posterior poles of the eyeball. anterior & posterior poles of the eyeball. visual axis is a straight line that joins the visual axis is a straight line that joins the center of the pupil & the fovea centralis. center of the pupil & the fovea centralis.
- 16. 16 16 The optical system of human eye: The optical system of human eye: Human eye is optically = photographic camera as Human eye is optically = photographic camera as it has a lens, a variable aperture (opening) it has a lens, a variable aperture (opening) system = pupil & film = retina. system = pupil & film = retina. The lens system is composed of 4 refractive The lens system is composed of 4 refractive interfaces: interfaces: 1. 1. Between air & anterior surface of the cornea. Between air & anterior surface of the cornea. 2. 2. Between posterior surface of the cornea & Between posterior surface of the cornea & aqueous humour. aqueous humour. 3. 3. Between aqueous humour & anterior surface of Between aqueous humour & anterior surface of the crystalline lens. the crystalline lens. 4. 4. Between posterior surface of the lens & the Between posterior surface of the lens & the vitreous humour. vitreous humour. The refractive index of air = 1, cornea = 1.38, The refractive index of air = 1, cornea = 1.38, aqueous humour = 1.33, crystalline lens = 1.40 & aqueous humour = 1.33, crystalline lens = 1.40 & vitreous humour = 1.34. vitreous humour = 1.34.
- 17. 17 17 Reduced or schematic eye: Reduced or schematic eye: If all refractive surfaces of the eye are If all refractive surfaces of the eye are algebraically added together, the eye acts as if it algebraically added together, the eye acts as if it is “reduced eye” having a single lens placed 17 is “reduced eye” having a single lens placed 17 millimeters in front of the retina. millimeters in front of the retina. The overall refractive power of the eye optical The overall refractive power of the eye optical system = 59 diopters, when the lens is system = 59 diopters, when the lens is accommodated for distant vision, accommodated for distant vision, 2/3 provided by 1/3 provided by 2/3 provided by 1/3 provided by anterior surface lens , approximately anterior surface lens , approximately Cornea, approximately = 20 diopters Cornea, approximately = 20 diopters = 40 diopters = 40 diopters