US 5,822,132 Example 1 — Asahi Optical / Hirakawa
| 5 elements / 5 groups |
| f = 28 mm |
| F/2.8 nominal; patent F.No. 1:2.9 |
| 2ω = 75° production; 75.8° patent |
| All-spherical soft-focus retrofocus |
Patent publishes infinity only. Close focus is modeled as inferred unit focus: final back-focus gap increases by about 5.04 mm from the Ricoh 0.18× maximum-magnification specification.
| Element | Type | Glass |
|---|---|---|
| E1 | Weak Biconvex Positive | N-SK5 / BACD5 class |
| E2 | Negative Meniscus | N-SK16 / S-BSM16 class |
| E3 | Biconvex Positive | S-LAH66 / N-LAF34 / TAF1 class |
| E4 | Biconcave Negative | J-SFS3 / SF56A class dense flint |
| E5 | Near-Plano-Convex Positive | S-LAH66 / N-LAF34 / TAF1 class |
Detailed analysis available in the interactive viewer above.