Characteristics and Uses of Lenses - Case Study Example

Lens and Fresnel lens A lens is a transparent material that is curved at the sides. The curving at the sides enables the concentration of light rays to form a beam. Mostly, the material used to make lenses is glass since it is transparent. The light rays converge as they pass through the biconcave lens at the top and diverge as they pass through a biconcave lens at the bottom. Lenses are used to change shapes and sizes of images received through it (Milton and Adrian, 99). Lenses can make images appear larger or smaller. Lenses are known to affect light focusing on a process called refraction. Refraction means the change of direction of propagation due to the change in the medium. If the medium is fast and light enters a slow medium, then refraction occurs. Through refraction, the light rays bend towards the normal to the boundary between the fast and the slow media. In addition to these type of lenses, other types can also refract radiations other than the visible light. Examples of such include microwave lenses and acoustic lenses. Lenses occur in various forms. The main difference between one type of a lens and the other is the shape, and the materials used to make the lenses. Converging lens is one of the types of lenses. These lenses cause rays that are parallel to come to a focus and produce a real image. They are also called positive lenses. The converging lens is always curved on both sides to enable the light rays that are coming out of it to come together at a point. The point where all the light rays meet or converge is called the focal point. If the image is outside the focal point, the image is always real and inverted. When the image is inside the focal point, the image then becomes virtual and upright. Convergent lenses are used in telescopes and binoculars so as to bring into focus distant light (Milton and Adrian, 85). Another type of lens is the diverging lens. Diverging lenses are those that cause a beam of light to diverge after a refraction. They are also called negative lenses. These types of lenses have a negative focal length (Milton and Adrian, 109). Divergent lenses have outer surfaces that curve inwards hence making the light rays to curve outward. The negative lenses work by diverging parallel beams of light and form a virtual image through extending light traces that are passing through the lens into a focal point that is behind the lens. The divergent lenses have a minimum of one concave surface. They are also thinner at the edges. When a negative lens is placed between the object and the eye, it reduces the apparent size of the object by forming a fake image implying that it does not form a real and authentic image. The reduction, therefore, brings the distinction between a real and a virtual image. Virtual images are formed when the light rays diverge but project imaginary extensions that then converge at the focal point. The virtual image can therefore not be seen on a screen or recorded on film although the observer views it as real image. On the other hand, real images are formed on the eye’s retina. The image in diverging lens is always virtual and is located between the object and the lens. Some of the gadgets using divergent type of lenses include television projectors, and car light bulbs. They help to make the beams of light spread into the distance. Fresnel lens is a lens that was developed by a French Physicist called Augustin-Jean Fresnel (Andrew and Judith, 34). He adopted this technology so as to use in lighthouses. The driving force and principal behind this intervention is that the direction of lights propagation does not change within a medium unless it is scattered. The light rays are instead diverted to the medium of the surfaces. Another reason that lead to the development of Fresnel lenses is because it was recognized that the contour of the refracting surface of a conventional lens always defines its focusing properties (Milton and Adrian, 64). It has a flat surface of concentric rings which aid and help reduce a spherical aberration. The Fresnel lenses are always arranged to make lightweight lens of a diameter and short focal length. Fresnel lens has the same mechanism with both the convergent and the divergent lenses. Fresnel lenses have a curvature that is concentrically divided by equal pitches. This division makes the lens smaller in volume and weight. Fresnel lenses are produced in different sizes ranging from small to large. Mostly, Fresnel lenses consist of a number of concentric grooves that are etched into a plastic. They have a thin, lightweight construction and also a very good light gathering ability that makes them useful in different applications. Fresnel lenses have grooves that act as individual refracting surfaces thereby making the lenses prone for solar concentration (Andrew and Judith, 46). In a Fresnel lens point of focus, there is extraction of a set of coaxial annular cylinders of materials because of the bulkiness of the material. The right circular cylindrical portions approximate the contour of the curved surface. However, it should be noted that these contours do not contribute to the lens’ optical properties. The properties are intersected by conical the grooves. Grooves are almost parallel to the plane face. The inclined surfaces, however, become more inclined towards the outer edge. In each groove, the inclined surface is the corresponding portion of the previous original aspheric surface that is translated towards the Plano surface of the lens. For the angle of the groove to compensate for the translation, there has to be a slight modification from that of the original aspheric profile. Fresnel lenses are mainly fabricated to make them correct for the case of grooves toward the collimated beam, that is referred to as grooves out. They can, however, be fabricated so that they are correct for the case of the grooves towards the focus, and is referred to as grooves in. For one to compress the surface power of the lens, one will require a finite prism pitch, a slope angle component that works to refract light rays in the desired and prescribed manner and a draft component that is optically inactive for the normal refractive lens. Fresnel lenses have got contours that act as individual surfaces. They do this by bending light rays to a common focal length. Due to this bending of light, Fresnel lenses are capable of concentrating light that is similar to a conventional optical lens (Andrew and Judith, 89). It, however, has several advantages over its thicker counterparts. Fresnel lenses can be manufactured or produced from different types of substrates. Mostly, the wavelength of operation will determine the content of the lens. Acrylic, polycarbonate, and vinyl are examples of the contents that are used to make the Fresnel lenses. The most common substrate is the acrylic since it has a very high transmittance in the visible and also in the Ultra Violet rays regions. Polycarbonate can also be preferred if there is a very harsh environment or surrounding since it is resistant to impact and high temperature (Milton and Adrian, 27). Fresnel lenses can be used to collimate light. Collimation of light is done through placing the lens one focal away from the source. The grooved side of the Fresnel lens ought to face the longer conjugate (Milton and Adrian, 13). Collimating lens thereby converts a point source to a beam of parallel light. Fresnel lenses are also applied in the collection of solar light which is referred as an infinite conjugate system. Through this, light is concentrated into a photovoltaic cell or heats a surface. When one decides to use a Fresnel lens with grooves, there is the disadvantage of lost light because of an incidence on the draft facet. During this, one should minimize the led draft-loss so as to make the facet perfectly vertical. If a Fresnel lens is used in any component of a display application or just any other type of application which the observer is looking through the lens, one must be careful and so should minimize the visual impact of the grooves. One can do this by ensuring he picks a facet that is pitch less than or else it can be equal to the human eye’s resolving power (Andrew and Judith, 107). In conclusion, lenses can be said to occur in different types and shapes. Lenses have different characteristics and uses. One of the characteristics is the color (Milton and Adrian, 95). High quality color lenses produce a subject’s natural color vividly as compared to the coated lenses that produce rich colors. Lenses that have a good tone produce very clear images. Contrast of the lens is another factor to be considered and so one should choose lenses that are of High contrast. This will ensure that the image has excellent transparency and it is also clear. One should also consider resolution since lenses with high resolutions produce perfect images from scantily detailed areas. When a lens has all the factors discussed, it becomes perfect and can be used in various ways like fitting in video cameras and iPhones so as to produce different effects and visuals. Works Cited Andrew G; Judith M. The contact lens manual: a practical guide to fitting. Edinburgh: Butterworth/Heinemann, 2010. Milton M H; Adrian S B. Manual of contact lens prescribing and fitting. St. Louis, Mo.Oxford: Elsevier Butterworth-Heinemann: Elsevier Butterworth-Heinemann, 2006. Read More