2The CameraThe ƒ-number of a camera is the ratio of the focal length of the lens to its diameterƒ = f/DThe ƒ-number is often given as a description of the lens “speed”The lowest ƒ-number setting on a camera corresponds to the aperture wide open and the maximum possible lens area in useM=h’/h=-q/ph’=-hf/pCamera with small f produces small images
3The Eye Essential parts of the eye Cornea – light passes through this transparent structureAqueous Humor – clear liquid behind the corneaThe pupilA variable apertureAn opening in the irisThe crystalline lensThe retinaThe retina contains receptors called rods and conesThe Eye
4Iris The iris is the colored portion of the eye It is a muscular diaphragm that controls pupil sizeThe iris regulates the amount of light entering the eye by dilating the pupil in low light conditions and contracting the pupil in high-light conditionsThe f-number of the eye is from about 2.8 to 16
5The Eye – Operation Rods and Cones Accommodation Chemically adjust their sensitivity according to the prevailing light conditionsThe adjustment takes about 15 minutesThis phenomena is “getting used to the dark”AccommodationThe eye focuses on an object by varying the shape of the crystalline lens through this processAn important component is the ciliary muscle which is situated in a circle around the rim of the lensThin filaments, called zonules, run from this muscle to the edge of the lens1/f = 1/p +1/q for an eye q=1.7 cm
6The Eye -- Focusing Lens maker’s formulae Lens equation When the eye focuses on a distant object, the ciliary muscle is relaxed and the zonules tighten, as a result the lens flattens, R1 and R2 increase.When the eye focuses on near objects, the ciliary muscles tenses, this relaxes the zonules, and the lens bulges a bit and the focal length decreases. The image is focused on the retina.
7The Eye – Near and Far Points The near point is the closest distance for which the lens can accommodate to focus light on the retinaTypically at age 10, this is about 18 cmIt increases with ageThe far point of the eye represents the largest distance for which the lens of the relaxed eye can focus light on the retinaNormal vision has a far point of infinity
8Farsightedness Also called hyperopia The image focuses behind the retinaCan usually see far away objects clearly, but not nearby objects
9Correcting Farsightedness A converging lens placed in front of the eye can correct the conditionThe lens refracts the incoming rays more toward the principle axis before entering the eyeThis allows the rays to converge and focus on the retina
10Nearsightedness Also called myopia In axial myopia the nearsightedness is caused by the lens being too far from the retinaIn refractive myopia, the lens-cornea system is too powerful for the normal length of the eye
11Correcting Nearsightedness A diverging lens can be used to correct the conditionThe lens refracts the rays away from the principle axis before they enter the eyeThis allows the rays to focus on the retina
12DioptersThe power of a lens in diopters equals the inverse of the focal length in metersP = 1/ƒ
13Problem 10.A PERSON HAS THE FAR POINT 84.4 CM FROM THE RIGHT EYE AND 122 CM FROM THE LEFT EYE. FIND THE POWERS FOR THE CORRECTIVE LENSES.
14The Size of a Magnified Image Angular magnificationis defined as
15Magnification by a Lens With a single lens, it is possible to achieve angular magnification up to about 4 without serious aberrationsWith multiple lens, magnifications of up to about 20 can be achievedThe multiple lens can correct for aberrations
16Compound MicroscopeThe image formed by the first lens becomes the object for the second lensThe image seen by the eye, I2, is virtual, inverted and very much enlarged
17Magnifications of the Compound Microscope The lateral magnification of the objective isL is the distance between the lensesThe angular magnification of the eyepiece of the microscope isThe overall magnification of the microscope is the product of the individual magnifications
18Telescopes Two fundamental types of telescopes Refracting telescope uses a combination of lens to form an imageReflecting telescope uses a curved mirror and a lens to form an imageTelescopes can be analyzed by considering them to be two optical elements in a rowThe image of the first element becomes the object of the second element
19Refracting TelescopeThe two lenses are arranged so that the objective forms a real, inverted image of a distance objectThe image is near the focal point of the eyepieceThe two lenses are separated by the distance ƒo + ƒe which corresponds to the length of the tubeThe eyepiece forms an enlarged, inverted image of the first image
20Angular Magnification of a Telescope The angular magnification depends on the focal lengths of the objective and eyepieceThe limiting angle of resolution depends on the diameter, D, of the aperture
21Reflecting Telescope, Newtonian Focus The incoming rays are reflected from the mirror and converge toward point AAt A, a photographic plate or other detector could be placedA small flat mirror, M, reflects the light toward an opening in the side and passes into an eyepiece
22Examples of Telescopes Reflecting TelescopesLargest in the world are 10 m diameter Keck telescopes on Mauna Kea in HawaiiLargest single mirror in US is 5 m diameter on Mount Palomar in CaliforniaRefracting TelescopesLargest in the world is Yerkes Observatory in WisconsinHas a 1 m diameter
23Resolution with Circular Apertures The diffraction pattern of a circular aperture consists of a central, circular bright region surrounded by progressively fainter ringsThe limiting angle of resolution depends on the diameter, D, of the aperture
24ResolutionFor the images to be resolved, the angle subtended by the two sources at the slit must greater than θmin
25QUICK QUIZ 25.2Suppose you are observing a binary star with a telescope and are having difficulty resolving the two stars. You decide to use a colored filter to help you. Should you choose a blue filter or a red filter?
26Michelson Interferometer One ray is reflected to M1 and the other transmitted to M2After reflecting, the rays combine to form an interference patternThe glass plate ensures both rays travel the same distance through glass
27Measurements with a Michelson Interferometer The interference pattern for the two rays is determined by the difference in their path lengthsWhen M1 is moved a distance of λ/4, successive light and dark fringes are formedThis change in a fringe from light to dark is called fringe shiftThe wavelength can be measured by counting the number of fringe shifts for a measured displacement of MIf the wavelength is accurately known, the mirror displacement can be determined to within a fraction of the wavelength
28Conceptual questions6. Compare and contrast the eye and a camera. What parts of the camera correspond to the iris, the retina, and the cornea of the eye?3. The optic nerve and the brain invert the image formed on the retina. Why do we not see everything upside down?8. If you want to use a converging lens to set fire to a piece of paper, why should the light source be farther from the lens than its focal point?7. Large telescopes are usually reflecting rather than refracting. List some reasons for this choice.9. Explain why it is theoretically impossible to see an object as small as an atom regardless of the quality of the light microscope being used.
29Problem 25.26A certain telescope has an objective of focal length cm. If the Moon is used as an object, a 1.0 cm long image formed by the objective corresponds to what distance, in miles, on the Moon? Assume 3.8 × 108 m for the Earth–Moon distance.
30Problem 25-48A person with a nearsighted eye has near and far points of 16 cm and 25 cm, respectively. (a) Assuming a lens is placed 2.0 cm from the eye, what power must the lens have to correct this condition? (b) Suppose that contact lenses placed directly on the cornea are used to correct the person’s eye. What is the power of the lens required in this case, and what is the new near point? [Hint: The contact lens and the eyeglass lens require slightly different powers because they are at different distances from the eye.]