Meniscus lenses are a type of imaging lens which has one convex and one concave surface. The result is a lens which has a positive focal length with fewer aberrations when compared to a plano-convex lens. Meniscus lenses are manufactured to either a positive or negative aspect. Positive meniscus lenses are those which have a shorter radius of curvature on the convex side and longer radius of curvature on the concave side; the edges of these lenses are thicker than its center. A positive meniscus lens can decrease the focal length of another lens but retain the angular resolution. Meniscus lenses are used to create a tighter beam focus. 

 

Negative meniscus lenses have a shorter radius of curvature on the concave side and a longer radius of curvature on the convex side; the center of the lens is thicker than its edges. This type of lens is frequently used in place of other negative lenses for high-index infrared materials. They are useful for beam-expanding applications which require minimal spherical aberration.

Selecting meniscus lenses 

Images credits: Newport; Nightlase Technologies