The best lens from where one conjugates is relatively for from the lens or where both conjugates are the same size of the lens.
The edge thickness of negative meniscus lens is bigger than center 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 |
