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glasses belong to the category of personal eye and face protection products. The technical indicators to measure their quality are mainly reflected in several aspects such as vertex power, UV protection, mechanical impact resistance, and whether they can block dazzling glare. 1. Measurement of vertex power For many years, there has been no uniform method for measuring vertex power of
sunglasses in the world. Different measurement results for the same product caused by different measurement methods, different measurement principles, and differences between different measurement instruments often occur, which triggers product quality disputes and then rises to technical barriers to trade, affecting international trade. As a major country in the production and use of sun
glasses, China has been using the focal meter method for many years. There are documents that have introduced the research results of the consistency of the measurement results between the telescope method and the focal meter method carried out by the China National Institute of Standardization. However, the new ISO/CD12311 '
Sunglasses-General Purpose Lenses' international standard and the European Union EN1836:2005 'Human Eye Protection
Sunglasses and Filters for Routine Use' recommend the use of the telescope method. At the meeting of the International Standardization Group ISO Sunglasses Measurement Method Standards Working Group held last year, the working group has written the focal meter measurement method proposed by my country into the ISO sunglasses testing method international standard. Vertex power measurement method and principle ①The telescope method accurately measures the optical power of sunglasses, that is, the reciprocal of the back focal length of the lens, and refers to the distance from the main surface of the lens to the back focus. The optical bench can be used to build an experimental platform for the telescope method. The experimental platform is mainly composed of 7 parts: light source, target resolution plate, diaphragm, stage, auxiliary lens, reading microscope, and guide rail. When measuring colored sunglasses, a white light source should be selected and ground glass should be placed behind the light source to make the beam uniform. When measuring non-band photometric lenses, a green broadband filter should be added in front of the light source to eliminate chromatic aberration and increase the comparability with the focal meter method. The ISO/CD12311 international standard recommends the use of a physical target with a fixed image. When measuring spherical flat sunglasses on the optical bench, an auxiliary lens should be added to the optical path to help the incident parallel light converge. The ISO/CD12311 international standard recommends the use of a 20 mm diaphragm for measurement. ②The focal power meter method measures the back vertex power of the lens, that is, the reciprocal of the back vertex focal length of the lens, and refers to the distance from the vertex of the back surface of the lens to the back focus. ③The definition difference derived from the two measurement principles. The difference in the definition of lens power and lens back vertex power. When the tested sample is a thick lens, its principal plane and back surface are not in the same plane, so the focal length Different from the rear vertex focal length, the derived optical power and rear vertex focal length are also different. Generally speaking, thin lenses can be ignored.
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