Bi-concave lens element

optical glasssapphirefused silica

A double concave lens/mirror has a negative focal length, thereby causing collimated incident light to diverge. The double concave lens/mirror has an equal radius of curvature on both sides of the lens. They are generally used to expand light or increase focal length in the existing system, such as beam expander and projection systems. Description Of Double Concave Lens/Mirror The double concave lens of Ecoptik has a negative focal length, thereby causing collimated incident light to diverge. A double concave lens has an equal radius of curvature on both sides of the lens.