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講者: 許永昌 老師 1 Contents Lenses in combination The Camera Vision Optical Systems That Magnify Magnifier Microscope Telescope The Resolution of Optical Instruments Aberration Diffraction resolution 2 Lenses in Combination (請預讀P739~P741) Purpose: Improve the image quality. Rule: The of the first lens acts as the for the second lens. (接物鏡, bigger) and (接目 鏡, smaller) 3 Lenses in Combination (continue) 1 1 1 , s1 s1' f1 1 1 1 ' , s2 s2 f 2 h1' s1' m1 . h1 s1 h2' s2' m2 . h2 s2 mnet=h’2/h1=m1m2. 4 The Camera (請預讀P742~P745) In this part, you will learn The configuration of a Camera. How to the combination lenses. by a f-number (a dimensionless number, f ). How to calculate The relation between . and f-number. How do a digital camera work? 5 The camera (continue) It consists of (lenses): the image on the detector. f ~6mm ~18mm. : m=-s’/s ~ f/s when s > 10f. : Control the (intensity and the energy per area). Dtshutter~ 1/1000 s ~ 1/30 s. f-number f/D. D: the diameter of the aperture. 2 D 1 : Why I ? : f2 f -number 2 Electronic light-sensitive surface called (CCD). 6 The Camera (continue) Change the effective focal length: Note: The we used here is that s when s > 10f. Reason: 1 1 1 , s s' f n sf f s' f , s f n 0 s when s 10 f , we get s ' ~ f . Action: Two students hold two lens and change the distance between these two lenses. Observe the change of the position of real image. 7 The Camera (continue) I=P/A 1/m2 1/f 2. Front view The same power Side view Aperture: Control the . IdetectorD2. Shutter: Control the . Their combination: Control the exposure (energy) per area. 8 Camera (continue) f-number: f f -number . D Notation: e.g. f-number = 4.0. f/4.0. F4.0. E.g. 1/125 F5.6 means Shutter time: 1/125 s f /D=5.6. 9 The Camera (final) The detector of a digital camera is charge-coupled device ( CCD ). 10 Homework Student Workbook 24.1 24.2 24.5 11 Vision (請預讀P745~P748) In this part you will learn The of a human eye and the each part. and . Vision defect and their correction. of : Find the correspondence between a human eye and a camera. 12 Vision (continue) The configuration of a human eye: Note: Cornea + Aqueous humor: lens in a Camera Lens: Adjust the focal length. 1. f-number of a human eye. 2. Why do everything will be very blurry if we open our eyes underwater? n=1.34 : n=1.44 n=1.34 1.5 ~ 8 mm 13 Vision (continue) Far point (FP) and Near point (NP): (FP): The farthest distance a Typical: m. can focus. (NP): The closest distance at which an eye can focus, using . Typical: ~ 25 cm (P7: s~10f). : Find NP of your eyes. 14 Vision (final) Vision defects: Presbyopia (老花眼) Hyperopia (遠視) Myopia(近視) Correction: By an extra lens: --- age, loss of accommodation. --- shortened eyeball. --- Elongated eyeball. The power of a lens: 1/f.(這不是功率) Unit: Diopter (屈光度): D: 1D= 1 m-1 =100度。 15 Homework Student Workbook 24.7 16 Optical Systems That Magnify (請 預讀P749~P753) In this part you can learn The concept of magnification for our eyes. The function of a magnifier. How do microscopes and telescopes work? : If the lens’s focal length is f and the incident angle is q, please tell me the position and height of image. q h’ s’ 17 Angular size and magnification We feel that something is magnified the is magnified is magnified. Example: Dmoom=3.48*106 m. dmoon to earth= 3.84*108m. q=D/d~ 0.01 rad Your arm ~ 1m; your thumbnail ~ 1cm. Therefore, the easiest way to magnify an object is that …………………??? Get closer. 18 Magnifier However, we cannot focus on the object if it’s closer than your near point.h q NP 25 cm it depends on the object’s height. Magnifier: Enhance the . The of a . Angular magnification: (簡言之,與肉眼所能看的最大放大率比) M q/qNP. : 如果眼睛貼著透鏡看s < f 的物體 呢?會如何? Hint: 角度&NP. (1) f > NP. (2) f < NP. q ~q M of a magnifier is defined while s~f M 25 cm f . 19 The Microscope and Telescope The is used as a simple the made by an lens. Microscope: M to view q q NP h mobj f eye h 25 cm mobj 25 cm f eye L 25 cm . f obj f eye Telescope: M q qin f obj f eye h ' f objqin f eyeq 20 Homework Student Workbook 24.8 21 The resolution of Optical Instruments (請預讀P753~P756) Since M=25 cm/f for a magnifier, it seems that we can use a single magnifier whose f is short enough as a microscope. However, it is not true. Two limitations: Any lens has : Chromatic aberration (frequency) Spherical aberration (angle) : The pattern of a parallel light focus on the lens’s focal point is a diffraction pattern; therefore it will be a spot instead of a point. 22 Diffraction again Mechanism: A lens both waves. and light These two effects are separable. The minimum spot size is wmin 2 f q1 2.44 f . D It becomes a limit of in the manufacturing of integrated circuits. Usually f D for realistic lens wmin 2.5. If the mask is projected with ultra-violet light having ~200nm, then the smallest elements on a chip are about 0.50 mm wide. 23 Resolution Telescope: : The two objects are resolvable if a > qmin=1.22/D. The two objects are not resolvable if a < qmin. The two objects are marginally resolvable if a = qmin. Microscope: d min 0.61 0.61 n sin a NA 不證。 : “看”得 到原子嗎? 24 Homework Student Workbook 24.10 Student Textbook 24.31 24.50 請自行製造本章的 terms and notation 的卡片。 25