The Positive Meniscus lens is used to decrease the focal length of another lens while maintaining the angular resolution of the optical assembly. They are commonly used to achieve tighter beam focusing paired with another positive lens.
These UF Grade Fused Silica positive meniscus lenses are designed to minimize spherical aberration. They have one surface convex and the other concave. When used in combination with another lens, a positive meniscus lens will shorten the focal length and increase the NA of the system.