What Is a Spherical Aberration?

Spherical aberration is caused by the difference in the ability of the central and edge regions of the electromagnetic lens to converge electromagnetic waves. The far-axis electromagnetic wave is refracted much more than the near-axis electromagnetic wave when passing through the lens. Therefore, the electromagnetic waves scattered by the same object point do not intersect at one point after passing through the lens, but become a diffuse circular spot on the lens phase plane. . Spherical aberration is the most important factor limiting the ability of a lens to resolve.

When the object distance L of the object point on the axis is determined, its image point position L 'is a function of the aperture angle U (or h). The difference between the position of the actual image point and the ideal image point is called spherical aberration. Spherical aberration (Spherical aberration)

The optical axes of light rays with different aperture angles U are at different points and have different deviations from the position of the ideal image point.

The light beam does not converge on an image point on the Gaussian image plane, but a circular diffuse spot.

Axial spherical aberration:

Spherical Aberration:

Rule of symbols: from the ideal image point to the actual light intersection

dL> 0 --- Positive spherical aberration:

The height h _{max of the} incident light corresponding to the maximum aperture angle U _max is called the full aperture (side light spherical aberration).

The vertical axis spherical aberration of the entire aperture beam forms a circular diffuse spot symmetrical to the optical axis on the image plane, which makes the imaging of the point on the axis blurred in severe cases. ^[3]

(1) Three positions where a spherical surface does not cause spherical aberration

(2) Qiming lens

(3) spherical aberration of single lens

(4) Combination of positive and negative lenses

A. The spherical aberration system generally can only make the spherical aberration of one aperture zero.

B. Spherical aberration is usually corrected for the edge aperture;

C. The spherical aberration of all apertures cannot be zero;

D. Negative spherical aberration-insufficient correction, positive spherical aberration-overcorrection.

Let the radius of curvature of a single refraction sphere be r and the refractive indices of the media on both sides be n ₁ and n _2. When the object point is at three positions, that is, the apex of the spherical surface (object distance u = 0), the center of the sphere and When the point determined by r * n ₂ / n ₁ does not cause spherical aberration, the latter two cases have important applications. Spherical mirrors have no spherical aberration only when the object point is at the vertex and the center of the sphere.

All rotating secondary aspheric mirrors have a pair of conjugate points that do not produce spherical aberration. Among them, parabolic mirrors are points and focal points on the axis of infinity; ellipsoidal mirrors and hyperbolic mirrors are their pair of focal points. They all have practical applications.