US 5,557,473 — Yoshikazu Sugiyama, Haruo Sato
| 6 elements / 6 groups |
| f = 28.60 mm |
| F/2.86 design |
| 2ω = 75.4° |
| all-spherical retrofocus |
Patent publishes only the infinity prescription; close focus is modeled as first-order unit extension by increasing BF from 38.09 mm to 43.17 mm at a 0.25 m metric reference state.
| Element | Type | Glass |
|---|---|---|
| L1 | Biconvex Positive | SF2-class dense flint (648/338; exact catalog identity uncertain) |
| L2 | Negative Meniscus | S-LAL7 (OHARA) |
| L3 | Biconvex Positive | J-LASF017 (Hikari catalog-equivalent to patent 797454; supplier not identified) |
| L4 | Biconcave Negative | SF56A (SCHOTT) |
| L5 | Positive Meniscus | S-LAL14 (OHARA) |
| L6 | Biconvex Positive | S-LAL8 (OHARA) |