US 1,975,678 — ZEISS IKON / LUDWIG BERTELE (1932)
| 7 ELEMENTS / 3 GROUPS |
| f ≈ 50.2 mm |
| F/1.5 |
| 2ω ≈ 46.8° |
| ALL SPHERICAL |
Unit focus — entire lens translates forward. BFD changes from 35.2 mm (∞) to 38.2 mm (0.9 m). Typical of 1930s Contax rangefinder mount lenses.
| Element | Type | Glass |
|---|---|---|
| L1 | Positive Meniscus | Dense Crown (SK/SSK family, Schott Jena) |
| L2 | Positive Meniscus | Barium Flint (BaF10 type, Schott) |
| L3 | Biconvex Positive | Specialty Low-Index Crown (hist. Schott, possibly fluoride-bearing) |
| L4 | Biconcave Negative | Dense Flint (SF family, Schott Jena) |
| L5 | Negative Meniscus | Light Flint (hist. Schott Jena) |
| L6 | Biconvex Positive | Very Dense Crown (SSK51 type, Schott) |
| L7 | Negative Meniscus | Crown (PSK3 type, Schott) |
Detailed analysis available in the interactive viewer above.