JP 2001-330771 A — Shizuka Takemoto, Norikazu Yokoi
| 10 ELEMENTS / 9 GROUPS |
| DESIGN f = 27.10 mm |
| DESIGN F/1.86 |
| 2 HYBRID ASPHERICAL SURFACES / 2 ELEMENTS |
| INFINITY FOCUS ONLY |
Infinity focus only; every air gap stays fixed. The patent describes floating focus in which both groups advance and the gap d11 ahead of the stop closes, and it tabulates one near state: d11 = 3.08 mm (6.81 mm at infinity) at an object 55 mm in front of the first surface, about 1:2.6, with the stop moving with the rear group. That state is not modeled because the patent prints no image distance for it. The 38.52 mm image distance at infinity is the paraxial back focus of the printed table; the patent prints no back focus. Sigma's 0.20 m minimum focus distance is product data, not modeled focus travel.
| Element | Type | Glass |
|---|---|---|
| L1 | Positive Meniscus | N-LAF35 (SCHOTT, coordinate equivalent) |
| L2 | Negative Meniscus | BASF7 (SUMITA, coordinate equivalent) |
| R1 | Hybrid resin negative meniscus | Unmatched (hybrid optical resin; spectrum unpublished) |
| L3 | Negative Meniscus | S-LAH51 (OHARA, coordinate equivalent) |
| L4 | Biconvex Positive | NBFD15 (HOYA, coordinate equivalent) |
| L5 | Positive Meniscus | NBFD15 (HOYA, coordinate equivalent) |
| L6 | Biconvex Positive | LAC8 (HOYA, coordinate equivalent) |
| R2 | Hybrid resin positive meniscus | Unmatched (hybrid optical resin; spectrum unpublished) |
| L7 | Positive Meniscus | K-LaK14 (SUMITA, coordinate equivalent) |
| L8 | Biconcave Negative | S-TIH4 (OHARA, coordinate equivalent) |
| L9 | Positive Meniscus | Unmatched (nd 1.60625, vd 63.1; no catalog match at the printed precision) |
| L10 | Biconvex Positive | Unmatched (nd 1.60625, vd 63.1; no catalog match at the printed precision) |