A meniscus lens is a concave-convex lens with one convex and one concave surface. If the convex curvature exceeds the concave curvature, the lens has a positive focal length and serves as a magnifier. Conversely, if the concave curvature is more pronounced than the convex curvature, the lens has a negative focal length. Such negatively curved meniscus lenses can replace other types of negative lenses.

The curved moon lens effectively minimizes spherical aberration to a greater extent. Compared to a plano-convex lens, the meniscus lens achieves a smaller focus and less distortion, enhancing image quality. When paired with another lens, a positively curved moon lens can shorten the focal length, thus increasing the system's numerical aperture (NA) without significant spherical aberration. For converging collimated light, position the convex side of the lens toward the light source.