Progressive film is also called progressive multifocal lenses, as the name suggests, there are a number of lenses on the focus.
If the focus is divided, the lens can be divided into a single focus lens, a double focus lens, multifocal lenses. We are the most common lens is single focus lens, the lens has a luminosity; double focus lens is double optical lenses, before a lot of old people used to solve problems at the same time to see near or far, but because the major disadvantage of itself and the gradual popularization of multi focus, bifocal lenses has basically been eliminated; multifocal lenses as the history of the development of a milepost on the lens, will also be the main direction of future development and market penetration of scientists.
