Types of glass - Binoculars
The optical system of binoculars is constructed from lenses made from glass and sometimes plastic. There are many types of glass available to manufacturers. All types of glass have their own advantages and disadvantages.
ED glass has a low dispersion, which helps to minimise the problems caused by chromatic aberration.
The prisms used in binoculars can be manufactured from BK7 glass. This is ordinary crown glass, which can be used to make prisms. However, a far more superior quality prism can be made from BAK-4 barium crown glass, a much more expensive material.
The choice of glass to be used in binoculars therefore depends partly on the optical requirements stipulated and partly on the price range into which the binoculars are to fall. The manufacture of binoculars remains a compromise! However, the difference in quality between binoculars with inferior quality optics and top-of-the-range binoculars with prime quality glass is very easy to discern. Contrast and image details can differ enormously.