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==Theory overview of a Fresnel lens==

==Theory overview of a Fresnel lens==

The principle behind a Fresnel lens is that the direction of propagation of light is not affected within a medium unless scattered. However, light rays deviate at the surfaces of a medium. This means that the majority of the material in the center of a lens only increases its weight and absorption within the system. <ref name=”2”></ref> <ref name=”3”></ref>

The principle behind a Fresnel lens is that the direction of propagation of light is not affected within a medium unless scattered. However, light rays deviate at the surfaces of a medium. This means that the majority of the material in the center of a lens only increases its weight and absorption within the system. <ref name=”2”></ref><ref name=”3”></ref>

A classical lens can become very heavy and expensive if the curvature and radius are sufficiently large. A Fresnel lens solves this since the light bending is essentially determined by the angle at the surface of the lens. The Fresnel lens has the same curvature at each point of incidence but is not as thick as a regular lens, achieving this by segmenting the classic lens and bringing together small segments of the right curvature. Almost every point in the Fresnel lens has the same curvature as a corresponding point in a classical lens. <ref name=”3”></ref>

A classical lens can become very heavy and expensive if the curvature and radius are sufficiently large. A Fresnel lens solves this since the light bending is essentially determined by the angle at the surface of the lens. The Fresnel lens has the same curvature at each point of incidence but is not as thick as a regular lens, achieving this by segmenting the classic lens and bringing together small segments of the right curvature. Almost every point in the Fresnel lens has the same curvature as a corresponding point in a classical lens. <ref name=”3”></ref>

==Fresnel Lens VR==

==Fresnel Lens VR==

With the popularization of VR and the commercialization of VR HMDs to the general public, Fresnel lenses have been integrated into some headsets to try to reduce their weight, thickness, and cost. The type of lens used in a VR headset is generally a factor that is overlooked when determining the HDMs’ quality. [[Virtual Reality Headset Lenses|Virtual reality headset lenses]] are important to help the viewer focus on the display’s images at close distances. <ref name=”3”></ref> <ref name=”5”>Visbit Inc. A guide to 360º virtual reality: part 2 - headsets. Retrieved from https://medium.com/visbit/a-guide-to-360%C2%BA-virtual-reality-part-2-headsets-5167a0d0870f</ref>

With the popularization of VR and the commercialization of VR HMDs to the general public, Fresnel lenses have been integrated into some headsets to try to reduce their weight, thickness, and cost. The type of lens used in a VR headset is generally a factor that is overlooked when determining the HDMs’ quality. [[Virtual Reality Headset Lenses|Virtual reality headset lenses]] are important to help the viewer focus on the display’s images at close distances. <ref name=”3”></ref><ref name=”5”>Visbit Inc. A guide to 360º virtual reality: part 2 - headsets. Retrieved from https://medium.com/visbit/a-guide-to-360%C2%BA-virtual-reality-part-2-headsets-5167a0d0870f</ref>

The standard lens used in almost all mobile VR headsets is a singlet. Compared to a Fresnel lens, singlets are thicker, heavier, and curved. High-end headsets like the [[HTC Vive]] use Fresnel lenses. The [[Oculus Rift CV1]] has hybrid Fresnel lenses. <ref name=”5”></ref> <ref name=”6”>VR Lens Lab (2016). How lenses for virtual reality headsets work. Retrieved from https://vr-lens-lab.com/lenses-for-virtual-reality-headsets/</ref>

The standard lens used in almost all mobile VR headsets is a singlet. Compared to a Fresnel lens, singlets are thicker, heavier, and curved. High-end headsets like the [[HTC Vive]] use Fresnel lenses. The [[Oculus Rift CV1]] has hybrid Fresnel lenses. <ref name=”5”></ref><ref name=”6”>VR Lens Lab (2016). How lenses for virtual reality headsets work. Retrieved from https://vr-lens-lab.com/lenses-for-virtual-reality-headsets/</ref>

In 2017, Wearality showed a prototype of a new Fresnel lens. The company already had developed a unique Fresnel lens for VR headsets, the Wearality Sky. The new lens is extremely thin and light, even when compared to those used in the high-end VR HMDs. <ref name=”7”>He, F. (2017). New Fresnel lens from Wearality is thinner than a quarter. Retrieved from https://www.roadtovr.com/new-fresnel-lens-wearality-thinner-quarter/</ref>

In 2017, Wearality showed a prototype of a new Fresnel lens. The company already had developed a unique Fresnel lens for VR headsets, the Wearality Sky. The new lens is extremely thin and light, even when compared to those used in the high-end VR HMDs. <ref name=”7”>He, F. (2017). New Fresnel lens from Wearality is thinner than a quarter. Retrieved from https://www.roadtovr.com/new-fresnel-lens-wearality-thinner-quarter/</ref>

The use of Fresnel lenses in VR is not without setbacks. Boger (2015) explains that “the main problem is what happens when light hits the ridges, those peaks in the lens that do not correspond to actual curvature in the original lens. When light hits these points it is scatted, and scattered light in an optical system reduces contrast. Thus, you will often see that a Fresnel lens produces a more “milky” image with lower contrast. The second problem is a more technical one – it is more difficult to simulate a Fresnel lens in an optical design software.” Creating a lens with many segments will lead to a sharper image, but light will be lost. Lenses with fewer segments will lose less light but the image produce will not be as sharp. <ref name=”3”></ref> <ref name=”6”></ref>

The use of Fresnel lenses in VR is not without setbacks. Boger (2015) explains that “the main problem is what happens when light hits the ridges, those peaks in the lens that do not correspond to actual curvature in the original lens. When light hits these points it is scatted, and scattered light in an optical system reduces contrast. Thus, you will often see that a Fresnel lens produces a more “milky” image with lower contrast. The second problem is a more technical one – it is more difficult to simulate a Fresnel lens in an optical design software.” Creating a lens with many segments will lead to a sharper image, but light will be lost. Lenses with fewer segments will lose less light but the image produce will not be as sharp. <ref name=”3”></ref><ref name=”6”></ref>

In the HTC Vive, the Fresnel lenses can occasionally show bright, concentric circles that can be distracting to the user. On the Oculus Rift, the hybrid Fresnel lenses can have the side effect of generating god rays. <ref name=”8”>Hutchinson, L. (2016). For this gadgethead, the HTC Vive may force my Oculus Rift to collect dust. Retrieved from https://arstechnica.com/gaming/2016/05/why-vive-has-won-the-early-vr-race-in-my-house/2/</ref>

In the HTC Vive, the Fresnel lenses can occasionally show bright, concentric circles that can be distracting to the user. On the Oculus Rift, the hybrid Fresnel lenses can have the side effect of generating god rays. <ref name=”8”>Hutchinson, L. (2016). For this gadgethead, the HTC Vive may force my Oculus Rift to collect dust. Retrieved from https://arstechnica.com/gaming/2016/05/why-vive-has-won-the-early-vr-race-in-my-house/2/</ref>