| 摘要 |
PURPOSE:To meter light in an objective space with a wide field angle by providing the external photometry optical system with three lenses and specifying the refracting power of the 2nd lens so that the exit pupil position of the 1st lens is conjugate to the entrance pupil of the 3rd lens. CONSTITUTION:The external photometry optical system is arranged at the periphery of a photography optical system, and the external photometry optical system consists of the 1st lens L1, the 2nd lens L2, and the 3rd lens L3. The refracting power of the lens L2 is so specified that the exit pupil position of the lens L1 is conjugate to the entrance pupil position of the lens L3. Further, the refracting power values of the lenses L1 and L3 are so specified that an image of a distant body is formed in the photometry system temporarily and then formed again outside of the photometry system. Then, a stop 21 for photometry is arranged at the image reformation position and its aperture diameter is controlled to adjust the quantity of light, so that luminous flux is guided to a photometric means 22 efficiently while field angle dependency is reduced. The stop 21 is arranged nearly on the same plane with a photography system shutter and the both are associated operatively with each other. Therefore, the luminous flux from the object space is guided to the photometry means efficiently to meter the light with high precision. |
