These lenses may be used to increase the numerical aperture of a positive lens assembly, without an undue increase in the aberrations.
The center thickness of positive meniscus lens is bigger than edge thickness.
| ATTRIBUTE | SPECIFICATIONS |
| material | N-BK7, Fused silica or specified |
| DIAMETER TOLERANCE | +0.0, -0.2mm |
| thickness TOLERANCE | +0.1, -0.1mm |
| radius | +/-0.1% |
| centration | < 3 arc minutes |
| SURFACE FIGURE: POWER(N) | <3 fringes |
| SURFACE FIGURE: IRREGULARITY(N) | <0.5 fringe |
| SURFACE QUALITY | 40/20 scratch and dig |
| Clear aperture | > 90% of diameter |
| BEVEL | < 0.2 mm x 45° |
| COATING | With AR coating on outside surfaces |
