In optics, by refractive index we mean the absolute refractive index. An index number is a number that tells us how many times a ray of light moves more slowly through an optical medium than in a vacuum.
In a vacuum, the speed of light is approximately 300,000 km/s. In the air, it slows down by 1.00029 times and that is the index of laziness. Refractive index is a number greater than or equal to 1 (n≥1). The index of refraction of optical lenses distinguishes between mineral and plastic lenses.
Mineral lenses have a refractive index of 1.5 to 1.9. As the index of refraction increases, the density of the lens increases and the thickness of the lens decreases. It is precisely with a high refractive index that it is possible to make a thin lens with a high dioptric power. Thinner mineral lens it does not necessarily mean that the lens is also lighter, because the density of mineral lenses increases with the increase in indexalom.
In practice, plastic lenses have taken the place of mineral lenses due to their resistance and lower density for the same refractive indices. Plastic lenses (CR) they have not yet been produced in refractive indices of 1.8 and 1.9, and thus we have not yet obtained the necessary lens thinness for plastic lenses. This is precisely one of the main advantages of mineral lenses with large diopters. Also, a thinner plastic (CR) lens does not mean that the lens is lighter because the density of plastic lenses increases with the increase in refractive index.
Author:
prof. Emil Šatalić
