| 摘要 |
The disclosed triplet type objective includes from front to rear, a first lens of positive power, a second lens of negative power and a third lens of positive power followed by a diaphragm, with at least one of the refracting surfaces of the second and third lenses being aspheric. To shape this aspheric surface with reference to a spherical surface for determining the focal length of the lens, numerical ranges are given for the axial distances between the aspheric and spherical surfaces at a maximum value and its half value for aspherical effectiveness from the optical axis. Satisfying these specified ranges makes it possible to correct all aberrations well, improve the compactness, and increase in the image angle.
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