am805 large bookmark magnifying glass

Fresnel lenses are made by pressing PVC material into shape based on the principles invented by French physicist FRESNEL. The lenses (0.45-0.5mm thick) have a circular groove engraved on their surface, starting small and getting larger, from shallow to deep, all centered around the same point, which looks like saw teeth when viewed from the cross section. The more concentric rings there are and the more densely engraved, the larger the sensing angle and the farther the focal distance; the deeper the concentric rings are engraved, the farther the sensing distance and the closer the focal distance. Several concentric rings in the same row form a vertical sensing area, and the concentric rings between them form a horizontal sensing segment. The more vertical sensing areas there are, the larger the vertical sensing angle; the longer the lens, the more sensing segments there are, and the larger the horizontal sensing angle will be.