Reference Guide

Lens Aberrations and Description
Type
1.
Chromatic Aber-
ration
1-1.
Longitudinal
Chromatic Aber-
ration
1-2_
Lateral
Chromatic Aber-
ration
2.
Spherical Aber-
ration
3.
Astigmatism
4.
Coma
5_
Distortion
6.
Curvature of
Field
Phenomenon
Illustration 1 a
white light _----+D~
~c
------\---"'I~
V
Illustration 1 b
Illustration 2
monochromatic light
i(»~
Illustration 3
Illustration 4
Illustration 5a
Illustration 5b
Illustration 6a
Illustration 6b
!f\-- - --
~ 7
/
/
Optical Principle (Definition)
1-1, An aberration that occurs from different indices of
refraction, according to the color of the light, wherein each
wavelength, e.g. a-wavelength, band c, has a different focal
point.
1-2, Image size differs according to wavelength. (Refer
to Illustration I-b)
• Impossible
to eliminate this by changing the aperture.
This aberration is caused by the sphericity of the lens. The
light does not focus at one point on the optical axis because
of the different indices of refraction.
(III ustration 2)
•
This can be corrected by stopping down the aperture,
but a shift in focus may result if the lens is stopped
down too much.
As the light from a point not on the optical axis passes
through the lens, it is focused as an image along different
tangential and sagittal focal lines.
(Illustrati'on 3)
• Though this can be slightly improved by stopping
down the aperture, this cannot be very effectively
compensated for.
The ray from a point not on the optical axis does not focus
on one po int of the image pi ane and there appears to be a
comet-shape. (Illustration 4)
•
This can be slightly decreased by stopping down the
aperture.
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CD
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A plane is not represented as being a plane.
A
square is distorted either in a barrel or
pin-cushion shape. The ideal image (Illustra-
tion 5a) should be an exact facsimile, like
A'B'C' vis-a-vis the subject ABC but the
distorted image is delineated as indicated
by A" C". (Illustration 5b)
• I mpossible to correct by changing the
aperture.
With ideal image definition (Illustration 6a), the subject ,
having
points A, B, C, on the same plane corresponds to
A', B', C' created on the image plane. If A' and C' do not
focus on plane B', but on different points A" or C", only B'
is in sharp focus while A" and C" are blurred.
• • Almost impossible to compensate for by changing the
aperture .