| Subject | English | German |
| phys. | curve of equal optical density | Äquidensite (of the first, second, n-th order) |
| phys. | equal-density curve | Äquidensite (of the first, second, n-th order) |
| phys. | equal-optical-density curve | Äquidensite (of the first, second, n-th order) |