US 5,321,555 A — Lothar Koelsch, Klaus-Dieter Schaefer
| 4 ELEMENTS / 3 GROUPS |
| DESIGN f = 33.63 mm |
| DESIGN F/3.5 |
| ALL SPHERICAL |
| ESTIMATED UNIT FOCUS TO 0.65 m |
ESTIMATED unit focusing. The complete four-element lens and rear iris move 1.958 mm toward the object at the brochure’s 0.65 m limit, interpreted from the image plane. Travel is calculated from this prescription; the patent prints infinity only and the actual camera mechanism is unconfirmed. Internal gaps stay fixed; intermediate positions interpolate nine calculated inverse-distance samples.
| Element | Type | Glass |
|---|---|---|
| L1 | Positive Meniscus | S-LAH65V (OHARA catalog equivalent; patent ne 1.808109 / νe 46.34; production supplier unspecified) |
| L2 | Negative Meniscus | S-TIH6 (OHARA catalog equivalent; patent ne 1.81264 / νe 25.23; production supplier unspecified) |
| L3 | Biconcave Negative | E-FD2 (HOYA catalog equivalent, catalog ne 1.65222 / νe 33.58; patent ne 1.65223 / νe 33.57; production supplier unspecified) |
| L4 | Biconvex Positive | LAFL4 (HOYA spectral proxy; catalog ne 1.716614 / νe 43.056 versus patent ne 1.7167 / νe 42.89; original type and production supplier unconfirmed) |