System and method for automatic engagement of a close-up lens in a fixed-focus camera
US5640635A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Oct 24, 1995 |
| Grant date | Jun 17, 1997 |
| Priority date | — |
| Expiry date | Oct 24, 2015 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG02B7/365
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
A fixed-focus camera having a retractable close-up lens, fixed-focus lens, infrared filter, and optical low-pass filter disposed along an optical axis within a housing. The close-up lens is switchable between a close-up position coaxial with the optical axis and a far position not coaxial with the optical axis. Light received from a target passes through an aperture in the housing and then through the lenses and filters. An image sensor receives the filtered light and outputs a two-dimensional array signal of corresponding voltages proportional to the energy of light striking each sensing element. The voltage signal from the image sensor is filtered using a high-pass filter and the high-frequency components of the signal are measured to determine a relative focal value for the light received from the target. The close-up lens is retracted for calculating a far-position focal value and then engaged for calculating a close-up position focal value, and the calculated focal values are compared to empirically-derived constant values to determine which lens position will produce a better-focused image.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.