Zoom lens of rear focus type
US5221994A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | May 29, 1992 |
| Grant date | Jun 22, 1993 |
| Priority date | — |
| Expiry date | May 29, 2012 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG02B15/144113
- WIPO fieldOptics
- WIPO sectorInstruments
Abstract
A zoom lens is disclosed, having four lens units of positive, negative, positive and positive refractive powers in this order from the object side, the focal length being varied by moving the second lens unit, and compensation for the image shift with zooming and focusing being performed by moving the fourth lens unit, while the first and third lens units remain stationary. The third lens unit has a positive first lens and a negative second lens having a concave surface facing the object side. The fourth lens unit has a negative first lens, a positive second lens and a positive third lens. The zoom lens satisfies the following conditions: EQU 0.54<f31/F3<0.7 EQU 1.35<N4P<1.67 EQU 51.8<.nu.4P<75 where F3 is the focal length of the third lens unit, f31 is the focal length of the positive first lens in the third lens unit, and N4P and .nu.4P are respectively mean values of the refractive index and Abbe number of materials of the second and third lenses in the fourth lens unit.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.