Lenses Have a Wide Variety of Uses - Research Paper Example

Lenses Lenses are used in practically all the aspects of human being’s life. The human eyes contain two lenses each,which enables them to focus and see things clearly. Lenses have a wide variety of uses and are not only used in correcting human vision, as they can be used to magnify and enhance objects that cannot be seen with the naked eye, with the help of telescopes and microscopes. This paper will examine the various types of lenses together with their properties and applications in real life. A lens can be defined as a transparent object containing two refracting surfaces that have central axes that coincide. The central axis of the lens forms the common central axis. Whenever a lens is surrounded by air, refraction of light takes place from the air into the lens, crossing through the lens and then refracting back into the air. Each refraction can lead to a change in the direction of light travel. There are two types of lenses, converging lenses, and diverging lenses. A converging lens is one that causes light rays that were initially parallel to the central axis to converge, while a diverging lens is one that causes such light rays to diverge. When an object is placed in front of any of the two types of lenses, light rays that can refract either into or out of the lens from the object to produce an image of the object. A lens can produce an object image only because it can bend light rays, but it can only do this only if its refraction index is different from that of the surrounding medium (Halliday, Resnick & Walker, 936). The single spot to which light rays that have been refracted by a lens are converging is known as the focal point. The distance from the lens to the focal point, often denoted by the letter f, is called the focal length. Every lens has its own focal length that forms its defining characteristic. A lens can have either a positive or a negative focal length, depending on the side of the lens on which an object is placed. When the focal point of a lens is on the opposite side of the lens from where an object is placed, the resulting focal length is positive. On the other hand, when the focal point is on the same side as the object, the focal length is negative. While these terminologies are useful convections used by scientists and engineers to characterize lenses as well as mirrors, they contain no real physical meanings (Kirkpatrick & Gregory, 367). Both converging and diverging lenses form different types of images, depending on where the object is placed. When an object is placed inside the focal point, the lens forms a virtual image that is on the same side of the lens as the object, and having the same orientation. Thus, a converging lens can form two types of images, real or virtual, depending on whether the object is placed inside or outside of the focal point. In the case of a diverging lens, the image formed is virtual that is on the same side of the lens as the object, and contains the same orientation. This is regardless of the object distance and whether it is placed inside or outside of the focal point. Just like in the case of mirrors, when the image is real the image distance is taken to be positive while when the image is virtual it is taken to be negative. However, the location from lenses of real and virtual images are the reverse of those belonging to mirrors. Real images form on the lens side that is opposite the object, while virtual images form on the side that the object is located (Benenson, 358). There are lens systems that are arrangements of a correction of lenses that have a common optical axis, and are mostly applied in the correction of image defects that are present in single lenses. If the positions of the principal planes of the single lens are known together with their total focus, then it is possible for an optical image to be constructed for a lens system. The image construction is similar with that of thick lens if there are only two principal planes. In addition to lens systems, there are lenses with diaphragms, whereby a diaphragm is a collimation of a light bundle. These types of lenses consists of aperture diaphragm that is a limit of rays generating an image, pupils that are generally diaphragms’ images, an entrance pupil that is the image of an optical system’s aperture diaphragm as seen from the side of the object, and an exit pupil that is the image of an optical system’s aperture diaphragm as seen from the side of the image (Benenson, 364). In the technical optics sense, the pupil of the eye is an aperture diaphragm, and an optical system’s aperture diaphragm must be chosen in a way that the exit pupil coincides with the position and size of the pupil of the eye. For eyeglass wearers using telescopes, microscopes and other optical objects, there exist special oculars with the exit pupil shifted backwards. It is important to note that all rays that pass through the entrance pupil must also pass through the exit pupil. There is always at least a diaphragm within a real lens system, which is the rim of the lens. The diameter of the lens determines what fraction of the rays that leave the object will be used in the formation of the image. The image brightness is determined by the dimensions of the diaphragm. A real image is normally projected within a screen, with the frame and dimensions of the screen determining the image size, and the frame representing the field diagram (Kirkpatrick & Gregory, 367). While lenses produce different types of images, there can occur image defects, or aberrations that are deviations of the light rays from their ideal paths. There are several types of image defects, each having its own consequences as well as ways of correcting it. Aperture aberration occurs when the light rays strike the lens system parallel but not close to the optical axis. Thus, the rays do not converge at the ideal focus. Consequently, if the paraxial rays and the rays that are far from the axis are simultaneously involved, the focus is widened to a definite size. This defect can be corrected by combining the lens with a diverging lens for the case of a converging lens, and vice versa. However, the correction can only work perfectly for a limited object distance. Another defect is known as astigmatism, which occurs in imaging of object points that are non-axial, as the refractive power of a spherical surface in the meridional section s different from that in the perpendicular sagittal section. This defect cases the image point to be ovally distorted, making the image to be blurred. It can be corrected through changing the positions of the diaphragms, as well as combining different lenses shapes made from different materials (Benenson, 365). Asymmetry defect, also known as coma, occurs when the incident bundle of rays that is oblique to the optical axis is blocked by a diaphragm. The image point is oval shaped and has a distortion that looks like a comet-trail. This defect is sensitive to and dependent on the shape and position of the diaphragm. The consequences of the defect are that it makes the image to be blurred and can be corrected through appropriately positioning the diaphragm and adding more lenses. Chromatic aberration occurs when the light applied in imaging is made up of different frequencies, with the lens system displaying dispersion, which is a frequency that depends on refraction. This defect causes each color to converge at its own focus, while the image is blurred and has edges that are colored. The defect can be corrected combining a converging lens with a diverging lens made of materials that have different dispersion behaviors, such as flint glass or crown glass. The correction is almost perfect when several glasses types are used together with multiple lens system (Benenson, 364). Works cited Benenson, Walter. Handbook of Physics. New York: Springer. 2002. Print Halliday, David., Resnick, Robert., & Walker, Jearl. Fundamentals of Physics, Part 4. New York: John Wiley & Sons. 2010. Print Kirkpatrick, Larry & Francis, Gregory. Physics: A World View. New York: Cengage learning. 2006. Print Read More