Double-concave lens, also named bi-concave or symmetric-concave lens, with two concave surfaces with identical radii, is used to diverge the collimated incident light and is best to use with the divergent incident light. A reduced sized virtual image will be seen through this lens. The materials can be BK7 or UV-grade synthetic fused silica. It is commonly used to expand light or increase focal length in optical systems. Bi-concave lenses are good to use on many devices of optical display/imaging systems and beam expanders etc. AR or NIR coatings can be order for specific applications.

Material--------------------BK7 Grade A or equivalent optical glasses

Design Wavelength-------480-650nm

Diameter Tolerance-------±0.1mm, ±0.15mm for Dia.≥75mm

Paraxial Focus Length-----±2% @546.1nm

Centration-----------------<3 arc minutes

Clear Aperture------------->80%

Surface Figure-------------λ/4 @632.8nm

Surface Quality------------60/40～40/20 scratches and dig

Coatings-------------------Antireflection coatings or NIR coatings

Bevel-----------------------A slight protective bevel