High Quality Product Ruler Book Mark Magnifier Ruler Card Magnifier in Plastic
Magnifying Ruler Bookmark
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Magnifying Ruler Bookmark Fresnel lenses are made of PVC material according to the principle invented by French photophysicist FRESNEL. The surface of the lens (0.45-0.5mm thick) is burned in concentric circles from small to large and outwards from shallow to deep, which looks jagged from the cross section. There are many circular lines and dense sensing angles, and the focal length is long; the deep induction distance of the circular line recording is long and the focal length is close. Several concentric rings in the same row form a vertical sensing area, and a horizontal sensing segment is formed between the concentric rings. The more the vertical sensing area, the greater the vertical sensing angle; the longer the lens, the more the sensing section, the greater the horizontal sensing angle.