Download Ch 24 Optical Instruments

講者： 許永昌 老師
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Contents




Lenses in combination
The Camera
Vision
Optical Systems That Magnify
 Magnifier
 Microscope
 Telescope
 The Resolution of Optical Instruments
 Aberration
 Diffraction
 resolution
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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)
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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=m1m2.
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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?
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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.
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D
1
: Why I 

?
:


f2
 f -number 
2
Electronic light-sensitive surface called
(CCD).
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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.
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The Camera (continue)

I=P/A  1/m2  1/f 2.
Front view
The same power
Side view
 Aperture:
 Control the
.
 IdetectorD2.
 Shutter:
 Control the
.
 Their combination:
 Control the exposure (energy) per area.
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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.
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The Camera (final)
 The detector of a digital camera is charge-coupled
device ( CCD ).
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Homework
 Student Workbook
 24.1
 24.2
 24.5
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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.
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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
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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.
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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。
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Homework
 Student Workbook
 24.7
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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’
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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.
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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
.
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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 
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Homework
 Student Workbook
 24.8
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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.
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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.
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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？
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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。
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