Meniscus Lens
Positive meniscus lens is a convex-concave lens thicker at the center than at the edges. It is used to minimize spherical aberration. When used in combination with another lens, it’s will shorten the focal length, and increase the NA of system.

Negative meniscus lens is a convex-concave lens thinner at the center than edges. It increases the divergence of the beam without introducing any significant spherical aberration. When used in combination with another lens, it will increase the focal length, and decrease the NA of the system.

Specifications:
Material: BK7 grade A optical glass
Design Wavelength: 546.1nm
Design Index: 1.5183+/-0.0005 at 546.1nm 
Diameter Tolerance: +0.0, -0.15mm(Standard), +0.0, -0.02mm(Precision)
Paraxial Focal Length: +/-2%
Centration: 3 arc minutes
Clear Aperture: >85%
Surface Figure: lambda/4 at 632.8nm
Surface Quality: 60-40 S/D
Bevel: 0.25x45deg