US 1,998,704 — Ludwig Bertele
| 6 ELEMENTS / 3 GROUPS |
| f ≈ 50.0 mm (scaled from 100mm patent) |
| F/2.0 |
| 2ω ≈ 46.8° |
| ALL SPHERICAL |
Inferred unit focus — all optics and the stop move objectward 3.16 mm at the modeled 0.90 m object-to-image endpoint. No focus schedule is published; intermediate distance labels are approximate.
| Element | Type | Glass |
|---|---|---|
| L1 | Positive Meniscus | Unmatched crown medium (patent optical constants; supplier unspecified) |
| L2 | Positive Meniscus | Unmatched (patent medium; supplier unspecified, patent nd=1.6711, νd=47.3) |
| L3 | Biconvex Positive | FK3 equivalent (catalog comparison; supplier unspecified) |
| L4 | Biconcave Negative | N-SF8 equivalent (catalog comparison; supplier unspecified, patent nd=1.6890, νd=31.2) |
| L5 | Negative Meniscus | Unmatched (patent medium; supplier unspecified, patent nd=1.5647, νd=55.8) |
| L6 | Biconvex Positive | Unmatched (patent medium; supplier unspecified, patent nd=1.6711, νd=47.3) |