Fresnel Lenses

Fresnel Lenses

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Fresnel Lenses

Fresnel lenses comprise a sequence of concentric grooves that are usually engraved into plastic. The thin and lightweight framework of the respective devices positions them as a useful form of lens in various applications aside from their other attributes such as the ease of accessibility and availability in a range of sizes. Accordingly, Fresnel lenses undergo applications considerably in light gathering paraphernalia such as detector or emitter setups as well as condenser systems. Aside from this, the respective devices can also be utilized as projection contacts within illumination systems or as magnifiers, especially in the formulation of clear images. In spite of the lack of importance associated with such facets, Fresnel lens are particularly significant based on the positive effects they impose due to their capabilities in capturing oblique light in contrast with other meniscus or contacts.

Original Development of Fresnel Lenses

The Fresnel lens was designed and initially developed by renowned French physicist, Augustin-Jean Fresnel. Originally, the lens was created for application in lighthouses. The application of the respective devices in such structures was rather beneficial since the light that usually emanated from the lighthouse was greater and more visible for persons or ships in longer and more expansive distances (Levitt, 2013). Despite the development of the lens under the guise of Augustin Jean-Fresnel, the concept involving the development of a lighter, thinner lens was exhibited by Comte de Buffon and Georges-Louis Leclerc. Both scientists proposed the idea of developing a lens by creating one with a collage of segregated segments mounted upon a frame. Additionally, more ideas focused on improving the physical design of lens by using glass as an effective medium for developing the much-needed device. In spite of this, Fresnel integrated such notions and managed to develop the multi-faceted lens, which was used largely in lighthouses.

In order to develop a significant lens for lighthouses of proper focal length, Fresnel considered advancing the size of the contacts. However, the concern surrounding the inability to support the weight of a twofold convex meniscus of that magnitude limited to fewer options. In this respect, the physicist came to the conclusion that size did nit assume any importance in lighting. In fact, the curvature of the surface was the sole factor that determined the degree of focusing power. As such, Fresnel focused on reproducing the curvature of the lens’ exterior into a collective of sections (Levitt, 2013). Despite the creation of different segments within the thick lenses, Fresnel focused on sustaining the same focal span with a part of the lens’ weight. Therefore, by dividing the thick lens into different sections with corresponding focal length, the physicist was capable of creating contacts or lenses that were capable of capturing the oblique light due to the increased strength of the focusing power.

The Premise behind the Fresnel Lenses

The main theory behind the development of this type of lens is based on the correlation between the medium and the direction attributed to the dissemination of light. Accordingly, the direction comprising the spread of light does not vary within an object. In fact, rays of light diverge at the exteriors of the respective medium or object (Greenslade, 2007). As an outcome, the volume or mass of the object within the center part of the Fresnel lens works solely in order to amplify the quantity of weight as well as absorption inside the system. Through experimentation, it was evident that the concentration of concentric grooves within a single piece of glass was important and strong in terms of the emission and capturing of light. Furthermore, the experimentation also established the basic importance of the surface width in relation to the dissemination and capture of light by the lens.

With the following considerations, the development of the Fresnel lenses immediately marked a new era in terms of light dissemination and gathering. Based on the significance of thinness, the lenses, which were etched on the glasses, possessed relatively thin surfaces, which were ideal for maintaining and establishing maximum focal power. Additionally, the grooves (normally present on the lens) were cut into glass in order to develop annular rings that comprised a curved lentil profile (Greenslade, 2007). Hence, a combination of both physical aspects and processes led to the development of a traditional, curved lens that was either spherical or aspherical depending on the way it was cut. Nevertheless, the properties that led to the formation of this particular meniscus established the Fresnel lens as a powerful meniscus and magnifier. In comparison to an optical lens, Fresnel lenses can provide stronger focusing performance in terms of the way in which they are applied.

Description and Function

Currently, Fresnel lenses decrease the quantity of material needed to develop a traditional lens by sectioning the respective surface into a collection of concentric ring-shaped segments. A common Fresnel lens tends to possess substantially many respective sections.  The Fresnel lens can be described as a range of prisms that are organized in a spherical manner, with an even or convex-based centre and vertical prisms around the edges (Greenslade, 2007). Interestingly, the same design was integrated in the first ever Fresnel lenses. Under the designs of the physicist Augustin-Jean Fresnel, the respective lenses (which were also large) possessed segments that comprised different prisms. However, after replication of the device over time, Fresnel lenses were produced that were smaller and single-pieced. Because of such modifications, the lenses could now be applied in smaller structures such as headlamps and signal indicators in automatic vehicles.

As asserted before, a normal Fresnel lens possesses substantially numerous concentric ring-shaped sections. Seemingly, in each segment, the general thickness or breadth is lessened in comparison to a corresponding simple lens (Greenslade, 2007). Hence, this successfully partitions or splits the continuous exterior of a normal lens into a collection of facades that possess the same curvature, with stepwise breaks between them. In other types of lenses, flat exteriors are used as substitutes for the curved surfaces. This eventually creates a range of prisms organized in a spherical manner. The design of the Fresnel lenses facilitates a cutback in terms of thickness. Even though the resulting product will be rather brittle and capable of easy breakage, such attributes are taken out in order to reduce the quality of the images on the lens. However, the reduction of the imaging preciseness supplements the refractive capabilities of the Fresnel lenses and allows for sharper focusing power.

Types of Fresnel Lenses

Overall, two forms of Fresnel lens exist based on their imaging capabilities. The first category comprises the imaging type. Imaging Fresnel contacts utilize sections that have curved cross-sections. The result of this constitutes the production of images with sharper resolutions in comparison to a normal Fresnel lens. Additionally, the imaging Fresnel lens runs the risk of maintaining a close similarity with its other form. This is because of the number of sections and the implications it imposes on the lenses’ abilities. Indeed, increasing the amount of segments establishes a considerable similarity with the non-imaging type of lens. A non-imaging Fresnel lens possesses flat surfaces in comparison to the imaging type. Because of such plane surfaces, the images produced by the respective lenses are weaker and not as sharp as those exhibited by the former type of lenses (Winston, 2012).

Imaging Fresnel contacts comprise spherical and cylindrical lenses (Winston, 2012). The spherical Fresnel lenses are similar in physical quality to a normal spherical lens. Spherical lenses tend to utilize concentric sections. Each of these sections comprises a spherical portion that facilitates the focusing of light onto a single focal point. The spherical Fresnel lenses produce sharper images. Cylindrical lenses, on the other hand, utilize straight sections and concentrate light on a sole line. Non-imaging Fresnel lenses comprise the spot and linear lenses (Winston, 2012). A spot Fresnel lens utilizes concentric sections that have cross sections constituted of straight lines. Even though the spot lens can concentrate light on a mark, the image produced is not sharp. Consequently, a linear Fresnel lens varies from the former type based on its incorporation of straight sections. Even though the respective sections also discard circular arcs, the lenses normally concentrate light by modifying them into thin bands.

Application and Conclusion

Due to their exclusive make-up, Fresnel lenses are used in a variety of applications. For instance, such devices are usually evident in the field of photography. Despite the thin and brittle nature of the lenses, the Fresnel lenses used in photography are beneficial particularly in terms of lessening the magnitude of the telephoto contacts (Edmund Optics, 2014). In addition, other cameras use the respective lenses as subsequent elements of their viewing frameworks. Fresnel lenses are particularly popular in the process of light collimation. Undeniably, such lenses can collimate a source by positioning it a focal span away from the point source (Edmund Optics, 2014). This in turn creates the best possible performance. In addition to collimation, Fresnel lenses are widely used in the gathering of solar light (Edmund Optics, 2014). Using this type of lens is perfect for focusing light on heating a surface or on a photovoltaic cell. For example, Fresnel lenses can be utilized for domestic maintenance activities such as heating a swimming pool or the internal area of a house. In conclusion, the Fresnel lens is a perfect illustration of the principle of refraction in action.

Appendix

Figure 1: Overall View of a Fresnel lens

(Retrieved from http://www.edmundoptics.com/technical-resources-center/optics/advantages-of-fresnel-lenses/)

Figure 2: Light Collimation (of a source using a Fresnel lens)

(Retrieved from http://www.edmundoptics.com/technical-resources-center/optics/advantages-of-fresnel-lenses/)

Figure 3: The Collection of Light (using a Fresnel lens)

(Retrieved from http://www.edmundoptics.com/technical-resources-center/optics/advantages-of-fresnel-lenses/)

References

Edmund Optics. (2014). Advantages of Fresnel lenses. Retrieved from http://www.edmundoptics.com/technical-resources-center/optics/advantages-of-fresnel-lenses/

Greenslade, T. B. (2007). Fresnel’s lighthouse lenses. The Physics Teacher/ American Association of Physics Teachers, 45, 550-551.

Levitt, T. (2013). A short, bright flash: Augustin Fresnel and the birth of the modern lighthouse. New York, NY: W. W. Norton & Company.

Winston, R. (2012). Nonimaging optics. New York, NY: Elsevier Academic Press.