optics - Focusing LED using a Fresnel lens at different distances - Physics Stack Exchange
What is Fresnel Lens? - FAQs | E-TAY INDUSTRIAL CO., LTD.
Energies | Free Full-Text | Simulation and Experimental Study on the Optical Performance of a Fixed-Focus Fresnel Lens Solar Concentrator Using Polar-Axis Tracking
Fresnel Lens Standard Range 15mm F.L. x 25mmdia aperture