US 3,536,379 — Georg Knetsch
| 3 ELEMENTS / 1 CEMENTED GROUP |
| 800mm f/6.3 MARKETED |
| PATENT MODEL f/5.9 |
Only the infinity state is published. The production minimum focus distance is 12.5 m; focus travel is not modeled.
| Element | Type | Glass |
|---|---|---|
| L1 | Negative Meniscus | Unmatched (Leitz proprietary/custom recipe; N-BAF10 coordinate-near only) |
| L2 | Biconvex Positive | Unmatched (Leitz proprietary fluorophosphate APD glass; exact recipe published) |
| L3 | Negative Meniscus | BaK4 (Jenaer Glaswerk Schott & Gen.; modern N-BAK4 coordinate-compatible) |