Chromatic aberration is the failure by a lens to concentrate all colors at the same point. Rays of varying colors are refracted to separate points because they have different wavelengths. An object with different colors will seem to merge at the edges due to this form of distortion. The refractive index of lenses differs with different wavelengths hence the occurrence of chromatic aberration. Different colors are focused at different points since the focal length depends on the refractive index. It is most evident at the boundaries separating bright and dark parts of an image (Atif 3).
Types of chromatic aberration
Chromatic aberration is classified as either axial (also known as longitudinal) or transverse (lateral) chromatic aberrations (BEDFORD, and WYSZECKI 67). Axial aberration is seen when different wavelengths are focused at points that are different distances from the lens but along the optical axis. Transverse aberration occurs when different wavelengths of light are focused are focused at different points on the focal plane (Aberrations par 4).
The two types of aberrations are different on various grounds but sometimes occur together. Axial aberration is evident throughout the image and is often minimized by stopping down in photography (Atif 3). Transverse aberration does not affect the image at6 the centre and is unaffected by stopping down (Smith 219).
Minimizing chromatic aberrations
The most common method of reducing chromatic aberrations is the use of a special form of a lens known as an achromat (Sasian 45). This is a lens that is formed by cementing two types of transparent materials to form the lens. The most common one is made from flint glass and crown glass. This method does not, however, eliminate aberration (Simonet, and Campbell 123). To further reduce the problem, more than two lenses of different compositions may be used (Aberrations par 4).
Alternatively, diffractive optical elements may be use to reduce chromatic aberration. These have a complementary effect to that of optical materials like glasses and plastics (Atif 3).
Recently, there are trends to minimize chromatic aberration in the processing room. An image that is delivered to the place with aberration is corrected to minimal errors. This method however may sometimes lead to loss of useful data in an image (Simonet, and Campbell 123). Chromatic aberration is reduced this way by cutting off the fringes of overlapping materials so that the remaining part overlaps correctly (BEDFORD, and WYSZECKI 67). Proper knowledge of the material used to take the image is sometimes very important in the removal process (Aberrations par 4).This process is not as good as that of using a lens that is corrected for aberration. It is usually associated with losing the resolution of the image made by the camera and inefficiency that results from lack the dyes made in digital cameras.
In conclusion, chromatic aberration is a type o0f distortion that disfigures the image that a photographer wants to deliver to his audience. For this reason, experts have a problem to solve. Several solutions have been identified including the use of achromatic lenses which is made of more than one type of material. Another method is the use of special materials known to have multiple reflective indices which all help to focus the image at the same point. The last opportunity for correction occurs in the processing room but is infamous for losing information photography data.
Aberrations. N.p., 2012. OpenStax CNX. Web. 21 June 2014. <http://cnx.org/content/m42292/1.2/>.
Atif, Muhammad. Optimal Depth Estimation and Extended Depth of Field from Single Images by Computational Imaging Using Chromatic Aberrations. S.l: s.n., 2013. Print.
BEDFORD, R. E., and G. WYSZECKI. “Axial Chromatic Aberration of the Human Eye.” Journal of The Optical Society of America (1957): n. pag. Print.
Sasian, Jose M. Introduction to Aberrations in Optical Imaging Systems. Cambridge: Cambridge University Press, 2012. Print.
Simonet, P., and M. C. Campbell. “The optical transverse chromatic aberration on the fovea of the human eye.” Vision Research (1990): n. pag. Print.
Smith, Warren J. Modern Optical Engineering: The Design of Optical Systems. New York: McGraw Hill, 2000. Print.
UV Rays and Infra Red Rays
Both infrared rays and ultraviolet rays belong to the electromagnetic spectrum. The electromagnetic spectrum shows all the possible wavelengths of electromagnetic radiations. It covers the all known electromagnetic waves from low frequency waves like radio waves to those of very high frequency like gamma radiations. The spectrum therefore covers radiations that have wavelengths of thousands of kilometers to those that are the extent of a part of an atom (GFELLER, and BAPST 23).
UV rays are radiations with a frequency higher than that of visible light. They have frequencies that range from 8×1014 to 3×1016 Hz and wavelengths between 10-8 m to 3.8×10-7 m. Exposure to these radiations for a long period causes sunburn and may cause skin cancer. Infrared rays, on the other side, have a lower frequency than visible light. Its frequency ranges between 3×1011 and 4×1014 Hz and have wavelengths from 7.5×10-7 m to 10-3 m. infrared radiation is commoner and is evolved by all bodies whose temperatures fall around body temperature as blackbody radiation. A high extent of UV rays may be harmful to the skin. As shown UV radiation is much shorter than IR radiation. Their effects to the environment are similarly diverse (GFELLER, and BAPST 23).
UV light has energies ranging from 3.10 eV to 12.4 eV. The high frequency UV has higher energy and even has ionizing effect when traversing through air. As it passes through air, it de-ionizes nitrogen molecules and di-oxygen molecules. This helps to absorb most of the high energy UV rays. Only the low energy rays reach the ground. IR energy on the other part has energies ranging from 1.24meV to 1.7eV. This energy is far lower than the energy of UV rays. The energy cannot be used to de-ionize substances. For this reason, while traversing through air, it does not help to de-ionize any of the molecules in air. UV rays are emitted or absorbed by molecules when their vibration moments are changed (Madronich, McKenzie, Björn, Caldwell, and Ilyas 46).
The velocity of both infrared and ultraviolet rays is similar to that of visible light and usually comes to around 2.998×108 m/s. They would move the same distance in a set amount of time. However, the infrared light would form fewer waves than UV.
Uses of UV light
UV light is used for checking for fake bank notes in some shops. It is also use for hardening some varieties of dental fillings. It is also used in clubs to make clothes glow. This happens as a result of the absorption of the UV light by some chemicals which are found in washing powder and then being emitted at a higher wavelength (Kingston 435).
The light is also used at security points to identify items marked using a special marker pen. They are also used to destroy microbes. They are therefore used in hospital to sterilize surgical equipments. Products in food companies may also be sterilized using UV light. UV light is associated with vitamin D and is used in small doses to treat deficiency of vitamin D and some forms of skin disorders.
Uses of IR light
Infrared radiations cannot be seen but can be felt on the skin. Infrared sensors are used for security alarms, and burglar alarms. It is also used for information transmission by mobile phones, computers and remote controls.
GFELLER, FRITZ R., and URS BAPST. “Wireless in-house data communication via diffuse infrared radiation.” Proceedings of The IEEE (1979): n. pag. Print.
Kingston, R. H. “Detection of Optical and Infrared Radiation.” (1978): Print.
Madronich, S., R. L. McKenzie, L. O. Björn, M. M. Caldwell, and M. Ilyas. “Changes in biologically active ultraviolet radiation reaching the Earth’s surface.” Journal of Photochemistry and Photobiology B-biology (1998): n. pag. Print.
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