Double concave lens, with a negative focal length, is commonly used for applications such as reducing beam size, reducing focal length, or enlarging images. To minimize spherical aberration, when using a double concave lens for collimated beam focusing, the beam should be incident on the lens surface; When used for point light source collimation, the beam is incident on both sides. Double concave lenses converge light to a focal point and are widely adopted for aiming and focusing monochromatic light sources. When used, the concave surface is facing the incident light. Double concave lenses coated with antireflection film, germanium, silicon or zinc selenide substrates are suitable for infrared applications, and fused silica is suitable for ultraviolet applications.

The two surfaces of a double-concave lens are concave, with the curvature centers located on either side of the lens.