When imaging with white light, in addition to five kinds of monochromatic aberration still produced by each monochromatic light, the dispersion caused by different refractive index of different colored light will also make different colored light have different propagation light paths, thus showing the aberration caused by the difference of light paths of different colored light, which is called chromatic aberration (abbreviated as chromatic aberration)chromatic aberration）。Color aberration is divided intoPositional chromatic aberrationandMagnification chromatic aberrationTwo.
actualoptical system There is a deviation between the actual image generated in the paraxial area and the ideal image generated in the paraxial area.At this time, the light beam emitted from any point on the object cannot converge into one point after passing through the optical system, and forms a diffuse spot, so that the image cannot strictly show the shape of the original object. This isaberration。
Chromatic aberration
brief introduction
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When imaging with white light, in addition to five kinds of monochromatic aberration still produced by each monochromatic light, the dispersion caused by different refractive index of different colored light will also make different colored light have different propagation light paths, thus showing the aberration caused by the difference of light paths of different colored light, which is called chromatic aberration (abbreviated as chromatic aberration)chromatic aberration）。Color aberration is divided intoPositional chromatic aberrationandMagnification chromatic aberrationTwo.[1]
Chromatic aberration
Positional chromatic aberration
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definition
Position chromatic aberration refers to the chromatic aberration that describes the difference of imaging position of the object point on the axis with two kinds of colored lights.
Chromatic aberration
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Picture of chromatic aberration of positive lens position:
Chromatic aberration diagram of positive lens position
Negative lens position chromatic aberration diagram;
Diagram of negative lens position chromatic aberration
Chromatic aberration seriously affects the imaging properties of optical systems. Generally, optical systems must correct chromatic aberration.The position chromatic aberration can be corrected by proper combination of positive and negative lenses.
Main factors affecting position color difference
(1) It increases with the increase of the aperture angle;
(2) It is related to the refractive index and dispersion index of optical materials;
(3) It is related to the focal length of the lens.
Magnification chromatic aberration
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definition
Power chromatic aberration is a kind of chromatic aberration caused by different image heights (i.e. power) of different color light.
It is measured by the difference in the height of the intersection point of the main rays of the two colored lights (i.e. F light and C light) on the Gaussian image plane
Indicates it.
give an example
Illustration of magnification color difference:
Graphic representation of magnification color difference
The magnification chromatic aberration increases with the increase of the field of view. Because of the existence of the magnification chromatic aberration, the edge of the object appears colored, thus causing the image formed by white light to appear colored spots.
For general optical systems, spherical aberration, coma and positional chromatic aberration have a great impact on the imaging properties, so first consider eliminating them. Since the human eye has the function of automatically correcting chromatic aberration, spherical aberration and coma mainly affect the imaging quality.
Main factors affecting magnification color difference
(1) It increases with the increase of field of view;
(2) It is related to the diaphragm position;
(3) Related to the refractive index and dispersion index of optical materials[2]
Monochromatic aberration
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classification
Spherical aberration -- wide beam aberration at the point on the axis;
Comet aberration -- wide beam aberration at off-axis point;
Astigmatism -- aberrations of fine beams at off-axis points;
Aberration generated when an axial object point is imaged with a wide beam.
The position of the image point formed by light with different aperture angles deviates from the ideal image point.
Since this spherical aberration is measured along the optical axis, it is also called axial spherical aberration.
Spherical aberration
Illustration of spherical aberration of positive lens:
Illustration of spherical aberration of positive lens
The existence of spherical aberration causes a diffuse spot on the image plane, and its radius is called vertical spherical aberration.
Main factors affecting ball error:
(1) It increases with the increase of square aperture angle;
(2) It is related to the shape of the lens;
(3) It is related to the focal length. The longer the focal length, the smaller the spherical aberration.[3]
Off-axis aberration
Comet aberration -- wide beam aberration at off-axis point;
Astigmatism -- aberrations of fine beams at off-axis points;
Image surface bending (field curve for short);
Distortion.
1. Huicha:
Coma
Meridional plane: The symmetry plane composed of the off axis object point B and the optical axis.
Sagittal plane: The face perpendicular to the meridian plane through the main light.
Main light: the light emitted from the off axis point B and passing through the center of the pupil.
(1) Meridian coma: the deviation from the intersection point BT 'of the upper and lower rays on the meridional plane to the main ray in the direction perpendicular to the optical axis, which is called the meridional coma, and is represented by the symbol KT'.
meridional coma
(2) Sagittal coma: the deviation from the intersection point BS' of the front and rear light lines on the sagittal plane to the main light in the direction perpendicular to the optical axis is called sagittal coma, which is represented by the symbol KS'.
Generation of distortion
For general practical optical systems, the vertical magnification is constant only in the paraxial region.When the field of view increases, the vertical magnification of the image will vary with the field of view, which will make the image lose its similarity with the original object.This kind of imaging defect that distorts the image is called distortion.
If the optical system has orthodontic deformation, that is, the actual image height is greater than the ideal image height, the resulting image is pillow shaped, and the negative distortion is barrel shaped.
Distortion only causes deformation and does not affect the image definition
The optical system distorts the vertical axis magnification of objects with different heights on the conjugate plane.
Generation of distortion
The image is distorted, but the definition of the image is not affected (due to different vertical magnification).
Significance of optical design
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Although the optical system has a series of aberrations, they can not be completely corrected and eliminated in general.However, because the human eye and all other light energy receivers also have certain sensitive defects, as long as the value of various aberrations is less than an allowable limit, the human eye and other light receivers still cannot detect or reflect the imperfections of their imaging.Such an optical system can be considered ideal in practical sense.
