Parallel light passes through a refractive substance, and the refractive power of the refractive substance is 1 diopter or 1D when the focus is1m.
The stronger the refractive power, the shorter the focal length. The focal length of a lens with 2D refractive power is 1/2m or 50cm. To know the focal length of the lens, divide 100cm, that is, 1.00m by the refractive power, and the result is the focal length.
For example, the focal length of 5D refractive power is 20cm. (100 cm divided by 5D = 20 cm. The refractive power of convex lens is indicated by "+",and that of concave lens is indicated by "-". 1 diopter or 1D equals 100 degrees.
Glasses degree = diopter × 100
Extended data:
As far as lens is concerned, it refers to the unit of lens power. If the focal length of a lens is 1m, then the diopter of this lens is 1D diopter and focal length or response.
The length of the focal length f represents the refractive power. The shorter the focal length, the greater the refractive power. The reason of axial myopia is that the imaging focus falls in front of retina due to the growth of axial length. People with hyperopia have too weak refraction.