Plano-Concave Lens has a negative focal length and is typically used to cause a collimated beam to diverge as in a Galilean type beam expander or Telescope. Because the spherical aberration of the Plano-Concave is negative, it can be used to balance the aberration of other lenses.

Specifications:
Material: Grade A optical glass or Fused Silica
Diameter Tolerance: +0.0, -0.15mm(Standard), +0.0, -0.02mm(Precision)
Paraxial Focal Length: +/-2%
Centration: 3 arc minutes
Clear Aperture: >85% of diameter
Surface Figure: Lambda/4@632.8nm
Surface Quality: 60-40 S/D
Bevel: 0.25x45deg