Optical aberration is an optical
phenomenon caused by the failure of a lens or mirror to produce a good image.

Overview
Deviation in optics indicates a defect in the lens so that the light does not focus on a point, but diffuses in some areas of space, so the image formed by a lens with aberration is blurred or distorted, with a distortion nature depending on the type of aberration.

And with the question of Dr. Muhammad Hantirah – Honorary Assistant Professor – Department of Ophthalmology – um Al-Qura University – Saudi Arabia

More specifically, it can be defined as the departure of the performance of an optical system from the predictions of the axial optics in the imaging system, which occurs when light does not converge from one point of an object to (or does not deviate from) one point after transmission through the system.

Deviations occur because simple axis theory is not a completely accurate model of the influence of the optical system on light, and not because of the defects of optical elements.
An optical system for forming images with a deflection will produce an image that is not sharp. Makers of optical devices need to correct optical systems to compensate for the deviation.

Deviation can be analyzed using geometric optics techniques. Articles on reflection, refraction and caustic substances discuss the general features of reflected radiation and refraction.

A phenomenon in which an image is blurred, distorted, or colored at the edge of an image even in the absence of a defect in the shape or material of the optical system when an image of an object is formed by an optical system such as a spherical lens or mirror.

The refractive index of glass is divided by the wavelength of wide spherical deviation and the light generated by monochrome light into different order chromatic aberration occurs. A wide spherical aberration, a narrow sensation of spherical deviation caused by the light emitted by a point object at one point of the image, coma, astigmatism, distortion of the surface of the image (the image of the plane object becomes curved) distortion of the image (the image of the square object becomes a shape in which the four sides swell outward or the four sides become a pointed shape with four sides marquee).

Since Seidel L. Seidel did a computational analysis in about 1850, this is called the five deviations of Seidel. In order to get as perfect a picture as possible by the visual system, these deviations should be small.