双凹透镜双面均为凹面，且具有相同的曲率半径。双凹透镜具有负焦距通常用于光束准直、增加（减小）焦距或扩大（缩小）图像。N-BK7是最常见的透镜材料
规格：
| 材料 | BK7, 融石英, CaF2 |
| 尺寸公差 | +0.0,-0.1mm |
| 中心厚度 | +/-0.2mm |
| 倒角 | <0.25mm |
| 近轴焦距 | +/-1% (EFL<1m) +/-2%（EFL>1m) |
| 光洁度 | 60-40 |
| 有效通光口径 | >85% |
| 镀膜 | 根据客户需求镀膜 |
| 型号 | 焦距f (mm) | 直径φ (mm) | 曲率半径R1=R2 (mm) | 中心厚度t c (mm) | 边缘厚度t e (mm) | 后焦距fb (mm) |
| LDC1101 | -25 | 12.7 | 26.25 | 2 | 3.6 | -25.7 |
| LDC1102 | -30 | 12.7 | 31.44 | 2 | 3.3 | -30.7 |
| LDC1103 | -40 | 12.7 | 41.80 | 2 | 3 | -40.7 |
| LDC1104 | -50 | 12.7 | 52.17 | 2 | 2.8 | -50.7 |
| LDC1201 | -25 | 25.4 | 26.25 | 2 | 8.6 | -25.7 |
| LDC1202 | -35 | 25.4 | 36.62 | 2 | 6.5 | -35.7 |
| LDC1203 | -50 | 25.4 | 52.17 | 2 | 5.1 | -50.7 |
| LDC1204 | -75 | 25.4 | 78.09 | 2 | 4.1 | -75.7 |
| LDC1205 | -100 | 25.4 | 104.00 | 2 | 3.6 | -100.7 |
