Aberration is a multi-valued term that is used in various fields of knowledge: astronomy, optics, biology, photography, medicine and others. What are aberrations and what types of aberrations exist will be considered in this article.
The meaning of the term
The word "aberration" comes from the Latin language and literally translates as "deviation, distortion, deletion". Thus, aberration is a phenomenon of deviation from a certain value.
In which scientific areas can aberration be observed?
Aberration in astronomy
In astronomy, the concept of light aberration is used. By it is meant the visual displacement of a celestial body or object. It is caused by the speed of light propagation relative to the observed object and observer. In other words, a moving observer does not see the object where he would observe it, while at rest. This is due to the fact that our planet is in constant motion, so the state of rest of the observer is physically impossible.
Since the phenomenon of aberration is caused by the displacement of the Earth, two types are distinguished:
- diurnal aberration: the deviation is caused by the diurnal rotation of the Earth around its axis;
- annual aberration: due to the revolution of the planet around the sun.
This phenomenon was discovered in 1727, and since then many scientists have paid attention to light aberration: Thomas Jung, Airy, Einstein and others.
Optical system aberration
An optical system is a set of optical elements that transform light beams. The most important system for humans of this kind is the eye. Also, such systems are used for the construction of optical devices - cameras, telescopes, microscopes, projectors, etc.
Optical aberrations are various image distortions in optical systems that affect the final result.
When the object moves away from the so-called optical axis, scattering of rays occurs, the final image is fuzzy, unfocused, blurred or having a color different from the original. This is aberration. When determining the degree of aberration, special formulas can be used to calculate it.
Lens aberration is divided into several types.
Monochromatic aberration
In a perfect optical system, the beam from each point of the object at the exit is also concentrated at one point. In practice, such a result is impossible to achieve: the beam, reaching the surface, is concentrated at different points. It is this phenomenon of aberration that determines the fuzziness of the final image. These distortions are present in any real optical system and it is impossible to get rid of them.
Chromatic Aberration
This type of aberration is due to the phenomenon of dispersion - light scattering. Different colors of the spectrum have different propagation velocities and degrees of refraction. Thus, the focal length is different for each color. This leads to the appearance on the image of colored contours or different colored areas.
The phenomenon of chromatic aberration can be reduced by using special achromatic lenses in optical instruments.
Spherical aberration
An ideal beam of light in which all rays travel through only one point is called homocentric.
With the phenomenon of spherical aberration, light rays passing at different distances from the optical axis cease to be homocentric. This phenomenon occurs even when the starting point is located directly on the optical axis. Despite the fact that the rays go symmetrically, the distant rays are more strongly refracted, and the end point acquires an inhomogeneous illumination.
It is possible to reduce the phenomenon of spherical aberration using a lens with an increased surface radius.
Distortion
The phenomenon of distortion (distortion) is manifested in the mismatch of the shape of the original object and its image. As a result, distorted contours of the object appear on the image. This distortion can be of two types: concavity of contours or their convexity. With the phenomenon of combined distortion, the image can have a complex character of distortion. This type of aberration is due to the distance between the optical axis and the source.
The phenomenon of distortion can be corrected by a special selection of lenses in the optical system. To correct photos, graphic editors can be used.
Coma
If the light beam passes at an angle with respect to the optical axis, then a coma is observed. The image of the point in this case has the form of a scattered spot resembling a comet, which explains the name of this type of aberration. When photographing, a coma often appears when shooting on an open aperture.
This phenomenon can be corrected, as in the case of spherical aberrations or distortion, by the selection of lenses, as well as by aperture - by reducing the cross section of the light beam using diaphragms.
Astigmatism
With this type of aberration, a point that is not on the optical axis can take the form of an oval or line in the image. This aberration is caused by different curvatures of the optical surface.
This phenomenon is corrected by selecting a special surface curvature and lens thickness.
These are the main aberrations characteristic of optical systems.
Chromosome aberrations
This type of aberration is manifested by mutations, rearrangements in the structure of chromosomes.
A chromosome is a structure in the nucleus of a cell that is responsible for the transmission of hereditary information.
Chromosome aberrations usually occur during cell division. They are intrachromosomal and interchromosomal.
Types of aberrations:
- deletion - loss of a chromosome site;
- duplication - doubling of the chromosome site;
- inversion - plot reversal;
- translocation - transfer of the site.
The causes of chromosomal aberrations are as follows:
- exposure to pathogenic microorganisms - bacteria and viruses that penetrate the structure of DNA;
- physical factors: radiation, ultraviolet, extreme temperatures, pressure, electromagnetic radiation, etc .;
- chemical compounds of artificial origin: solvents, pesticides, salts of heavy metals, nitric oxide, etc.
Chromosomal aberrations lead to serious health consequences. The diseases they cause are usually named after the specialists who described them: Down Syndrome, Sherchevsky-Turner Syndrome, Edwards Syndrome, Klinefelter Syndrome, Wolf-Hirschhorn Syndrome and others.
Most often, diseases provoked by this type of aberration affect mental activity, skeletal structure, cardiovascular, digestive and nervous systems, and the reproductive function of the body.
The likelihood of these diseases is not always possible to predict. Nevertheless, already at the stage of perinatal development of the child, with the help of special studies, one can see the existing pathologies.
Aberration in entomology
Entomology is a branch of zoology that studies insects.
This type of aberration manifests itself spontaneously. Usually it is expressed in a minor change in the structure of the body or the color of insects. Most often, aberration is observed in Lepidoptera and Coleoptera.
The causes of its occurrence are the impact on insects of chromosomal or physical factors at the stage preceding the imago (adult individual).
Thus, aberration is a phenomenon of deviation, distortion. This term appears in many scientific fields. Most often it is used in relation to optical systems, medicine, astronomy and zoology.