| 摘要 |
PURPOSE:To obtain a long focus optical system which has an ultra-large aperture and satisfactorily corrected aberrations and which is easily worked by providing the system with four optical elements and satisfying specific conditions. CONSTITUTION:Viewed from the object side, the titled system is composed of the 1st optical element E1 consisting of a menisucul lens with a weak negative power, the 2nd optical element E2 consisting of a reflecting surface with positive power, the 3rd optical element E3 deflecting reflected light from the 2nd optical element, and the fourth optical element 4 containing to least one negative lens. They have to be constituted to satisfy the condition shown by inequalities I where f, f1, RI,1, fII and lII,III denote the focus distance of the entire system, that of the 1st optical element, the curvature radius of the 1st face of the 1st optical element, the focus distance of the 2nd optical element and the air interval from the 2nd optical element to the 2nd one, respectively. Thus, such a high performance reflecting and refracting optical system can be obtained that is composed of easily worked spherical systems. The cost of the optical system is advantageous and its spherical aberration, coma aberration and astigmatism are minimized.
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