Plano concave lens has a negative focal length, diverges collimated incident light from one another on the output side of the lens and hence have a negative focal length, and forms only virtual images which are seen through the lens. It is often used to expand light beams or increase focal lengths in existing systems. Because the spherical aberration of the Plano-Concave lenses is negative, they can be used to balance aberrations created by other lenses.
| ATTRIBUTE | SPECIFICATIONS |
| material | N-BK7, Fused silica etc |
| DIAMETER TOLERANCE | +0.0, -0.2mm |
| Central thickness tolerance | +0.1, -0.1mm |
| radius | ±1% |
| CENTRATION | <3 arc minutes |
| CLEAR APERTURE | >90% |
| SURFACE FIGURE: POWER(N) | <3 fringes |
| SURFACE FIGURE: IRREGULARITY(N) | <0.5 fringe |
| SURFACE QUALITY | 40/20 scratch and dig |
| BEVEL | < 0.2 mm x 45° or protective bevel |
| COATING | With or without coating |
