Fresnel lens characteristics

It's a convex lens.If the light source is parallel, the corners will become dark and fuzzy, because the refraction of light only occurs at the interface of the medium, the convex lens is thicker.The part of the glass where light travels in a straight line attenuates the light.If the part of linear propagation can be removed and the brightness of the image can be kept the same throughout the image after convergence projection, a large amount of materials can be saved to achieve the same focusing effect at the same time.Fresnel lenses use this principle. Fresnel lenses look like a piece of glass with an infinite number of concentric circles (known as Fresnel bands).