| 摘要 |
PURPOSE:To prevent making a field lens larger and to realize a high precision focal point detecting device by providing a reflecting plane on the part of the field lens and reflecting luminous flux incident on the lens peripheral area by using the reflecting planes and conducting light to a secondary optical system. CONSTITUTION:Light quantity distributions at the plural regions of an object image formed by an objective lens 1 are conducted to photodetector strings 5a, 5b..., etc., by a secondary optical system 4, and the focusing condition of the objective lens 1 is obtained. The field lens 3, which permits almost conjugate relationship to the pupil of the objective lens 1 and the pupil of the secondary optical system 4, is Fresnel shaped corresponding to every range-finding region in the direction where plural range-finding regions 2a-2e are provided by the opening of a visual field mask 2, and the field lens 3 permits planes 3a and 3e on the peripheral part to be the reflecting planes. Since the luminous flux incident on the peripheral part of the field lens 3 is reflected by such reflecting planes and conducted to the secondary optical system 4, the enlargement of the field lens in the case of making the diameter of the field lens larger is prevented. |
