Chap. 2 Principles of optical instruments

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Chap. 2 Principles of optical instruments
?????????
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• 2.1 Magnifying power of aided visual instruments
  Magnifying glass
  
• 
  
  ????????? ???
• 2.2 Huygens eyepiece and Ramsden eyepiece
• 
  ???????????
  
• 2.3 Magnifying power of microscope
  ????????
• 2.4 Magnifying power of telescope
  ????????
• 2.5 (Optical) Stop/diaphragm and pupil
  ?? ??
• 2.6 Outline of photometry-transmission of light
  energy
• 
  
  ?????
• 2.7 Light gathering power of objective
  ???????
• 2.8 Aberrations
  ????

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Preface
Human eye
??construction of human eye ?????
(looked as optical instrument)
In the view of geometric optics,
Some norms
Pupil ??control the luminous flux entering the
human eye.
Crystalline humorthe convex lens with adjustable
focal length.
???
Retinaaccept the image.
???
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??reduced eye
From the point of geometric optics, human eye can
be looked as coaxial lenses with different
mediums. So it can be simplified as a reduced
eye of a spherical surface .
n1
n'4/3
F'
f '22.8mm
??adjustment function of human eye

Far point8
??
Normal eye ???
Near point(changes with the age)
??
Distance of distinct vision 25 cm
????
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Myopic eye Nearsighted eye
Hyperopic eye Farsighted eye
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Abnormal eye
Myopic eye ??? the far point is finite,
correcting through
the concave lens
Hyperopic eye??? the near point goes further,
correcting
through the convex lens
Astigmatic eye ???curvature of cornea is
inhomogeneous
???????
Unit diopter1/m
Focal power
???
1/?
???
??100???
Degree100 diopter
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2.1 Magnifying power of aided visual instruments
Magnifying glass
??The concept of magnifying power
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1. Sensing of human eye to the size of object
Q
??????????
u
-l
P
Visual angle u is subtended by the object at the
human eye
??????????u
2. Magnifying power
Q
Q'
u'
-l'
P
P'
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lthe image length on the retina without aided
instrument.
l' the image length on the retina with aided
instrument.
u'the visual angle with aided instrument.

Far objectthe visual angle is subtended by the
object at the human eye.
(telescope)
u
Near object the visual angle is subtended by the
object , which is put at the
distance of distinct vision

(microscope)
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??amplifying lens / magnifying glass ???
y'
y
u'

F
-p'
y
u
25 cm
Magnifying power of lens
?
3
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2.2 Huygens eyepiece and Ramsden eyepiece
??function of eyepieces
Large magnifying power, Broad field of
view, Correct the aberration.
Functions
Eye lens ???(??)

An eyepiece consists of two or more thin lenses
Field lens ???(??)
??two kinds of eyepieces
1. Huygens eyepiece ?????
L1
L2

objective
H'
H
F
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Remove the chromatic aberration
combine
???
properties
(1) achromatism ????
(2)Huygens eyepiece can only be placed after the
objective, and magnify the image
which is in the distance of distinct
vision. ???????,????????,?????
(3)large field of view
2. Ramsden eyepiece ?????

H'
H
F
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combine
Properties
(1) Ramsden eyepiece can be directly used as
magnifying glass.
?????????
(2)Comparing with Huygens eyepiece, Ramsden
eyepiece can be directly used as
magnifying glass, While Huygens
eyepiece can only observe the image.

(3)The system is relatively long.
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2.3 Magnifying power of microscope
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Simplify into a lens
? l(length of a tube ??)
small f1' , f2
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Magnifying power of microscope
?
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2.4 magnifying power of telescope
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reflectorreflecting telescope
Objective Large f1'

lensrefracting telescope
telescope

convexKeplers telescope
eyepiece
??,???
??????
concaveGalileos telescope
??????
??Keplers telescope/ Keplerian telescope
The object at infinity
? 0
F1'
F2
u

-y1
-u'
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Magnifying power
?
Mlt0,inverted image
Finite object
F1'
F2

u
-u'
Magnifying power
?
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??Galileos telescope/ Galilean telescope
objective
Magnifying power
Mgt0, erect virtual image
??reflecting telescope(astronomical telescope)
Now,
Newtons telescope ????????
Schmidt telescope
??????
Gregorys telescope ????????
Hubble space telescope ???????
Cassegrains telescope ????????
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??Extender instrument of laser ?????
Convergence point can produce ionization
Upside-down Galilean telescope ?????????
supplement
???????????????????????????10cm,???????3?,??????
f1,f2 ?
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2.5 (Optical) Stop/diaphragm and pupil ?? ??
??The concept of stop/diaphragm
Stopthe plate with loophole of optical system
???
Function
?Effective diaphragm/stop limit the aperture
angle
of object on the axis

Classifying ( function)
????
?????????
Field diaphragm/stop limit the paraxial image
formation
??????
?????
????
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??Effective stop(aperture stop) and pupil
????(????)
Effective stoplimit the entrance beam most of
all stops
???????,????????????????
For the point of axis
P1effective stop


Q
P
Q2effective stop
1
2
Properties
(1)varies with different specific object points
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A'
A
ABis the effective stop of point P


P
P'
B
B'
(2)limitation of image ray can be looked as
the limitation of object ray.

Entrance pupil????limit entrance rays,
the image of effective stop by former system
??????,????????????????
Exit pupil ????limit exit rays,
the image of effective stop by latter system
??????,????????????????
Either real object or image
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2.6 Outline of photometry-transmission of light
energy
????????? ????????
??Radiant flux ????
Radiant flux e ?????,????????????????
(unitW)
Radiation flux density e(?)???????????????
???????
v(?)
??Visibility function
standard luminosity curve
1.0
????
??????
properties
?
(1)varies with different persons
555nm
(2)varies with background brightness
(if the background is dark, it moves to the short
wave.)
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??Luminous flux F
???
Luminous fluxit is only that part of the total
radiation flux, which is visible and can affect
the eye.
unitlumen (lm
??????
Km
Km 683 lm/W
luminous flux of homochromatic light
luminous flux of polychromatic light
Luminous efficiency
??????
????
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??Intensity of illumination ????
Intensity of illuminationluminous flux per unit
solid angle
??????????????? ????????????
unitcd (candle)
SI?,????????
If the intensity of illumination of a source in
all directions, then
??????????????????, ????????5.401014
Hz?????, ?????????????1/683 W/sr?
(sr????)
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??Incidence and exitance
??????
Illuminance Ethe flux per unit area incident
onto
a real or imaginary surface.
unitlux, lm/m2
???????????
???
Point light source
R
dS
Surface light source
Exitance Mthe flux emitted per unit area of a
source
of radiation. ?????????????
unitlux, lm/m2
???
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??Illuminating power ??
Illuminating power Lthe luminous flux per unit
solid angle
per unit projected area.
??????????,??????????????
S
unitcd/m2
By the definition of intensity of illumination,
we have
???????,L???
Expansive light source dI? cos?
Lamberts cosine law
????
L is independent of ?
Lambert source
????
Diffuse reflection
Lambertian reflector
????
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??Principle of three primary colors ?????
The light of nature can be mostly obtained by
the combining of different proportional luminous
flux of three colors.
???????????????????????
Photoelectric conversion
discompose
Colorful kinescope
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2.7 Light gathering power of objective ???????
Light gathering power of objective is the
physical quantity of the ability to gather the
luminous flux.
?? light gathering power of microscope,
numerical aperture
Illuminance of image surface
????
L0illuminating power of object in the vacuum
?transverse magnification
u
RN.A.numerical aperture
n the refractive index of object
u aperture angle
???
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?? Light gathering power of telescope, relative
aperture
???????? ????
Illuminance of image surface
d objective aperture of telescope
d/f 'relative aperture
Reflecting telescope 1/3.33
d/f '
Refracting telescope 1/18.9
?? Light gathering power of camera

Far object
Illuminance of image surface
Near object
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F number (???)the reciprocal value of relative
aperture,
F ?
that is, f '/d
Generally,F 1K presents the relative aperture
of objective.
?????DF????
F 12
F number f '/d
1 1.4 2 2.8 4 5.6 8
11 16
Relative aperture d/f '
1/1 1/1.4 1/2 1/2.8 1/4 1/5.6 1/8
1/11 1/16
Illuminance of image surface
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2.8 Aberrations ??
Classification of aberrations
Monochromatic aberrations
Chromatic aberrations
Point of paraxial
Point of axis (broad beam)
Near point ( broad beam )
Far point (sharp beam)
The refractive index of the material of a lens
is different for different wavelengths.
distortion
Spherical aberration
coma
astigmatism
???????????????????
Curvature of field
Barrel distortion
Pincushion distortion
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Chromatic aberration
??
Constringence(V?)
?????,???
nDyellow refractive index
nFblue refractive index
nCred refractive index
Remove chromatic aberration
???
1. Combination of two different materials
2. Two lenses are made of the same material
Satisfy,
then,
Chap. 2