US 2,279,384 — Fred E. Altman
| 5 ELEMENTS / 3 GROUPS |
| f ≈ 100.36 mm |
| F/4.5 |
| 52° FULL FIELD |
| ALL-SPHERICAL |
Unit focus by enlarger bellows or lens-stage movement; the close-focus state is a representative 3× enlarger conjugate.
| Element | Type | Glass |
|---|---|---|
| L1 | Biconvex Positive | Unmatched (vintage barium crown class, 611/572) |
| L2 | Biconcave Negative (weak rear) | BAK1 (SUMITA catalog equivalent for patent coordinate; production supplier unspecified) |
| L3 | Biconcave Negative | Unmatched (vintage dense flint class, 605/382) |
| L4 | Negative Meniscus | Unmatched (vintage light flint class, 575/414) |
| L5 | Biconvex Positive | Unmatched (vintage high-index lanthanum flint class, 744/458) |