林正峰 10/7/2008
實驗三講義
光學像差的觀察
 Spherical aberration（球差）
Ray striking the surface at greater distances above the optical axis are focused nearer the
vertex.
For a single refracting spherical interface,
Paraxial region:
n1 n2 n2  n1
,


s o si
R
Third-order theory:
n
n1 n2 n2  n1


 h2  1
s o si
R
 2so
2
 1 1
n
    2
2si
 so R 
1 1
  
 R si 
2

.

The aberration term, which varies approximately as h2, is clearly a measure of the deviation
from the first-order theory.
 Longitudinal spherical aberration (LSA)
The distance between the axial intersection for a ray and the paraxial focus (Fi).
For a converging lens, LSA is positive.
For a diverging lens, LSA is negative.
 Traverse (or lateral) spherical aberration (TSA)
The height above the axis where a given ray strikes the screen at Fi.
 Circle of least confusion
If the screen is moved to the position labeled LC, the image blur will have its smallest
diameter. This disklike spot is called the circle of least confusion.
If a screen is placed at Fi, the image of a star will appear as a bright central spot on the axis
surrounded by a symmetrical halo delineated by the cone of marginal rays.
SA can be reduced by stopping down the aperture.
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林正峰 10/7/2008
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林正峰 10/7/2008
(a)
(b)
(a): Images of a point source produced by an optical system with increasing amounts of
spherical aberration. (b): Images of a distant star formed by the HST.
 Chromatic aberrations（色差）
The chromatic aberration arises from the fact that refractive index of the lens is
wavelength-dependent.
-Axial chromatic aberration (ACA)
Horizontal distance between the axial images.
Positive: blue focus is to the left of red focus, positive lenses
Negative: blue focus is to the right of red focus, negative lenses
-Lateral chromatic aberration (LCA)
Vertical difference in height of images.
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Axial chromatic aberration
Lateral chromatic aberration
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