Positive meniscus lenses are used to decrease the focal length of another lens while maintaining the angular resolution of the optical assembly. These lenses are commonly used to achieve tighter beam focusing when paired with another positive lens. Positive meniscus (convex-concave) lenses causes light rays to converge, are designed to minimize third-order spherical aberration. When used to focus a collimated beam, the convex side of the lens should face the source to minimze spherical aberration.