Characteristics and solutions of lens aberration

On aberration of lens

I have been playing with binoculars and cameras for more than a year, during which I also learned a lot of useful knowledge from the internet and forums. A few days ago, I bought "Photography Optics and Lens" written by Mr. Yuan Kai. I looked at it carefully and found it was quite good. The article about lens aberration is similar to binoculars, so I now choose it to share with the vast number of equipment lovers.

An ideal lens should be able to form a clear image point for each object point on the object plane at the corresponding position on the image plane within the full effective field of view, but the actual objective lens cannot form an ideal image anywhere on the image plane, and the difference between the actual image and the ideal image formed by the objective lens is called aberration. Common aberrations can be divided into "monochromatic aberration" and "chromatic aberration".

Monochromatic aberration: Monochromatic aberration refers to the aberration formed by light of a single color passing through a lens, which can be divided into the following categories:

1, spherical aberration

A beam of light parallel to the lens optical axis or at a small angle to the optical axis is called paraxial light. When paraxial light passes through a spherical lens, the light passing through the center of the lens and the light passing through the edge of the lens cannot intersect at one point. This aberration is caused by the spherical surface of the lens, so it is called spherical aberration. The longer the focal length, the larger the relative aperture and the more serious the spherical aberration. The spherical aberration makes the Ming Rui spot become a fuzzy spot, and the size and brightness distribution of the spot also change with the position of the film. Using aspheric lens can effectively reduce spherical aberration, in addition, aspheric lens can also reduce distortion and simplify the lens structure.

Characteristics of spherical aberration: spherical aberration is a unique aberration of paraxial light, which mainly appears in the center of the picture. The longer the focal length, the more obvious the spherical aberration. When the spherical aberration is large, the imaging position of the lens will also change with the change of aperture. No matter what the characteristics of spherical aberration are, it can be improved quickly after reducing the aperture.

Step 2 be in a coma

A beam of oblique imaging light with a large angle to the optical axis is called far-axis light. When off-axis light passes through a lens, it cannot converge at one point, and often forms a comet-like spot, so this aberration is called coma. There are many ways to reduce coma, but coma is a very stubborn aberration. Even after trying to eliminate the primary coma, it often produces a smaller but more complicated secondary coma.

Characteristics of coma: Coma is a unique aberration of far-axis light, so it mostly occurs at the edge of short-focus lens, and it is difficult to completely eliminate coma. Reducing the aperture can reduce coma.

Step 3 Astigmatism

When a thin beam of off-axis light passes through the lens, it will be focused into two tiny focal lines at different spatial positions, one along the radial direction from the center of the picture to the edge, which is called radial focal line or sagittal focal line, and the other along the circumferential direction centered on the center of the picture, which is called tangential focal line or meridian focal line. The really focused image point is in the middle of two focal lines, which looks like a fuzzy spot. Because the two focal lines are separated from each other, this aberration is called astigmatism. Astigmatism makes the lines on the edge of the picture have different sharpness in meridian and sagittal directions.

Characteristics of astigmatism: Astigmatism is also the unique aberration of off-axis light and the most stubborn aberration. Not only is it difficult to eliminate, but it has nothing to do with aperture. It is difficult for us to reduce astigmatism by narrowing the aperture, so astigmatism often becomes the focus of monochromatic aberration when evaluating the imaging quality of a lens.

4. The image surface is curved

When the object plane perpendicular to the optical axis is imaged, the image plane becomes a curved surface, which is called image plane curvature, also referred to as image field curvature or field curvature. When a lens with a curved image plane images a plane object, it is impossible to aim at the focus of the middle and peripheral parts of the picture at the same time.

Usually, we call the plane composed of smaller intermediate spots between the meridian focal line and the sagittal focal line as the image plane, so there is often astigmatism in the curvature of the image plane. The curvature of image plane is not only accompanied by the difference in the definition of center and edge, but also the obvious difference in the resolution of meridian and sagittal direction at the same position in the image field.

Step 5 deform

The image of a straight line becomes a curve, which is called distortion. According to the direction of straight line bending, distortion can be divided into pillow distortion (also known as pillow distortion) and barrel distortion (also known as negative distortion). Distortion is also accompanied by changes in image size. The actual image of pincushion distortion is larger than the theoretical value, and the actual image of barrel distortion is smaller than the ideal image. Distortion is usually caused by asymmetry between the optical structure of the lens and the aperture position. In addition, the position of the aperture in the lens will also affect the characteristics and magnitude of distortion. Aspheric lens can not only eliminate spherical aberration, but also improve distortion.

Distortion characteristics: in the center of the field of view, the distortion is zero; Generally, the farther away from the center of the picture, the greater the distortion; The straight line passing through the center of the image field is undistorted. Distortion does not affect the sharpness of the lens, and it has nothing to do with the aperture size.

On aberration of lens

On aberration of lens

I have been playing with binoculars and cameras for more than a year, during which I also learned a lot of useful knowledge from the internet and forums. A few days ago, I bought "Photography Optics and Lens" written by Mr. Yuan Kai. I looked at it carefully and found it was quite good. The article about lens aberration is similar to binoculars, so I now choose it to share with the vast number of equipment lovers.

An ideal lens should be able to form a clear image point for each object point on the object plane at the corresponding position on the image plane within the full effective field of view, but the actual objective lens cannot form an ideal image anywhere on the image plane, and the difference between the actual image and the ideal image formed by the objective lens is called aberration. Common aberrations can be divided into "monochromatic aberration" and "chromatic aberration".

Monochromatic aberration: Monochromatic aberration refers to the aberration formed by light of a single color passing through a lens, which can be divided into the following categories:

1, spherical aberration

A beam of light parallel to the lens optical axis or at a small angle to the optical axis is called paraxial light. When paraxial light passes through a spherical lens, the light passing through the center of the lens and the light passing through the edge of the lens cannot intersect at one point. This aberration is caused by the spherical surface of the lens, so it is called spherical aberration. The longer the focal length, the larger the relative aperture and the more serious the spherical aberration. The spherical aberration makes the Ming Rui spot become a fuzzy spot, and the size and brightness distribution of the spot also change with the position of the film. Using aspheric lens can effectively reduce spherical aberration, in addition, aspheric lens can also reduce distortion and simplify the lens structure.

Characteristics of spherical aberration: spherical aberration is a unique aberration of paraxial light, which mainly appears in the center of the picture. The longer the focal length, the more obvious the spherical aberration. When the spherical aberration is large, the imaging position of the lens will also change with the change of aperture. No matter what the characteristics of spherical aberration are, it can be improved quickly after reducing the aperture.

Step 2 be in a coma

A beam of oblique imaging light with a large angle to the optical axis is called far-axis light. When off-axis light passes through a lens, it cannot converge at one point, and often forms a comet-like spot, so this aberration is called coma. There are many ways to reduce coma, but coma is a very stubborn aberration. Even after trying to eliminate the primary coma, it often produces a smaller but more complicated secondary coma.

Characteristics of coma: Coma is a unique aberration of far-axis light, so it mostly occurs at the edge of short-focus lens, and it is difficult to completely eliminate coma. Reducing the aperture can reduce coma.

Step 3 Astigmatism

When a thin beam of off-axis light passes through the lens, it will be focused into two tiny focal lines at different spatial positions, one along the radial direction from the center of the picture to the edge, which is called radial focal line or sagittal focal line, and the other along the circumferential direction centered on the center of the picture, which is called tangential focal line or meridian focal line. The really focused image point is in the middle of two focal lines, which looks like a fuzzy spot. Because the two focal lines are separated from each other, this aberration is called astigmatism. Astigmatism makes the lines on the edge of the picture have different sharpness in meridian and sagittal directions.

Characteristics of astigmatism: Astigmatism is also the unique aberration of off-axis light and the most stubborn aberration. Not only is it difficult to eliminate, but it has nothing to do with aperture. It is difficult for us to reduce astigmatism by narrowing the aperture, so astigmatism often becomes the focus of monochromatic aberration when evaluating the imaging quality of a lens.

4. The image surface is curved

When the object plane perpendicular to the optical axis is imaged, the image plane becomes a curved surface, which is called image plane curvature, also referred to as image field curvature or field curvature. When a lens with a curved image plane images a plane object, it is impossible to aim at the focus of the middle and peripheral parts of the picture at the same time.

Usually, we call the plane composed of smaller intermediate spots between the meridian focal line and the sagittal focal line as the image plane, so there is often astigmatism in the curvature of the image plane. The curvature of image plane is not only accompanied by the difference in the definition of center and edge, but also the obvious difference in the resolution of meridian and sagittal direction at the same position in the image field.

Step 5 deform

The image of a straight line becomes a curve, which is called distortion. According to the direction of straight line bending, distortion can be divided into pillow distortion (also known as pillow distortion) and barrel distortion (also known as negative distortion). Distortion is also accompanied by changes in image size. The actual image of pincushion distortion is larger than the theoretical value, and the actual image of barrel distortion is smaller than the ideal image. Distortion is usually caused by asymmetry between the optical structure of the lens and the aperture position. In addition, the position of the aperture in the lens will also affect the characteristics and magnitude of distortion. Aspheric lens can not only eliminate spherical aberration, but also improve distortion.

Distortion characteristics: in the center of the field of view, the distortion is zero; Generally, the farther away from the center of the picture, the greater the distortion; The straight line passing through the center of the image field is undistorted. Distortion does not affect the sharpness of the lens, and it has nothing to do with the aperture size.