Chromatic Aberration in a Lens

In the study of lens, we always consider that the image obtained is perfect size, contour and color. However, in reality it is not so because when considering rays in reality we need to consider both paraxial as well as marginal rays owing to which a image can never be perfect. This difference between an image formed by a lens and the object in terms of shape, size, color etc. is known as aberration. Now aberration is of two types-monochromatic aberration and chromatic aberration. To understand the latter we need to concentrate on a prism first. A prism splits white light into its seven constituent colors. While violet light suffers maximum deviation and deviates towards the base of the prism while red color suffers the minimum deviation. The refracting angle of a prism is greatest at its center and reduces towards the sides. When white light is incident on the prism, each light is deviated at a different angle and thus they focus at different points on the principal axis. This results in the formation of a blurred and colored image. This defect in image formation is termed as chromatic aberration. Now, a lens is considered to be made up of a number of prisms and hence this prismatic phenomenon of chromatic aberration when shown by the lens is known as chromatic aberration in a lens.
Consider a convex lens on which a beam of white light is incident. Dispersion takes place and the white light is split up into its constituent colors and each of the colors is focused at different positions on the axis. This gives a blurry image. A concave lens also shows a similar phenomenon and forms an unclear image. Chromatic aberration in a lens is again of two types-longitudinal and lateral. Longitudinal aberration is the difference between the focal lengths of violet and red color. Lateral chromatic aberration is the difference in the magnification of the image formed by the red and violet light rays.
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Infrared radiations and Ultraviolet rays
The electromagnetic spectrum consists of different types of electromagnetic waves all arranged according to their frequencies or wavelengths. Infrared radiation and ultraviolet radiations belong to the electromagnetic spectrum. Ultraviolet rays are emitted by the atoms during their transitions from one state to another. Infrared radiations are produced by atoms during state transitions and also by molecules during rotational transitions. Due to difference in atomic transitional energies, both infrared radiations and UV rays have different photon energies. The photon energy of UV rays is between 3 eV – 124 eV (electron Volt) while the photon energy of infrared radiations lies between 1.24 meV- 1.7 eV The wavelength of Ultraviolet rays is shorter than that of visible light and ranges between 10 nm – 400 nm while the wavelength of infrared rays is longer than that of visible light and ranges between 750 nm – 1 mm. However only their velocities in air are same and are equal to that of visible light in air.
Both of these rays are utilized for different purposes. UV rays are utilized for studying photoelectric effect and analyze their interaction with living cells. In laboratories, these rays are used to eliminate all forms of microorganisms. UV lamps are also used cautiously for treating skin diseases such as psoriasis and vitiligo. In fact the production of vitamin D in our body depends on exposure to this ray. UV rays finds use in the forensic studies as well and helps to analyze or detect body fluids.
Infrared radiations too have a wide number of uses. They are used for hyperspectral imaging, short range communication and study the structure of molecules though IR spectroscopy. They are also use in climatology studies to analyze and understand global warming phenomenon.
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