US 721,240 — Paul Rudolph
| 4 ELEMENTS / 3 GROUPS |
| f ≈ 144 mm (scaled from normalized patent) |
| F/5.5 |
| 2ω ≈ 60° |
| ALL SPHERICAL |
Unit focusing — entire lens assembly moves forward. No variable internal spacings. Front-element focusing also used on mid-range cameras (L1 moves ~⅓ the distance of unit focus due to ~2.8× power ratio).
| Element | Type | Glass |
|---|---|---|
| L1 | Plano-Convex Positive | Dense barium crown (Schott ~O.381, SK-type) |
| L2 | Biconcave Negative | Dense flint (Schott ~O.163, F/SF-type) |
| L3 | Biconcave Negative | Light crown / light flint (Schott ~O.332, K/LLF-type) |
| L4 | Biconvex Positive | Dense barium crown / barium flint (Schott ~O.382, SK/BaF-type) |