A Fresnel lens replaces the curved surface of a conventional lens with a series of concentric grooves, molded into the surface of a thin, lightweight plastic sheet. The grooves act as individual refracting surfaces, like tiny prisms when viewed in cross section, bending parallel rays in a very close approximation to a common focal length. Because the lens is thin, very little light is lost by absorption. Fresnel lenses are a compromise between efficiency and image quality. High groove density allows higher quality images, while low groove density yields better efficiency (as needed in light gathering applications). In infinite conjugate systems, the grooved side of the lens should face the longer conjugate.
Fresnel lenses are most often used in light gathering applications, such as condenser systems or emitter/detector setups. Fresnel lenses can also be used as magnifiers or projection lenses; however, due to the high level of distortion, this is not recommended.
菲涅耳透鏡以輕量級塑膠薄膜表面模壓成型的一系列同心溝槽，取代了傳統透鏡的曲面。這些溝槽可充當單獨的折射面 (以橫截面檢視時與微稜鏡相似)，能將平行光以極為近似的方式折向共同焦距。由於透鏡很薄，所以因吸收而損失的光線量很少。菲涅耳透鏡可兼顧效率與影像品質的要求。高溝槽密度有助於改善影像品質，而低溝槽密度則可提升效率 (符合聚光應用的需要)。在無限共軛系統中，透鏡刻有溝槽的一側應面向較長的共軛。
菲涅耳透鏡在聚光應用 (例如聚光系統或發射器/偵測器設備) 中最為常用。菲涅耳透鏡還可以用作放大鏡或投影透鏡，但是由於畸變度高而不建議使用。