| 摘要 |
PURPOSE:To make a lens system compact and to compensate fairly the coma and astigmatism of the lens system by setting specific conditional formulas among intervals of lens faces, refractive indexes, a focal length, and radiuses of curvature in the lens system consisting of three groups of four lenses. CONSTITUTION:The lens system consists of a positive meniscus lens, a double concave lens, a double convex lens, and a negative meniscus lens arranged in order from the object side, and the third and fourth lenses are stuck, that is, the lens system consists of three groups of four lenses. Formulas I-VIII are set among intervals (d) of lens faces, refractive indexes (n), a focal length (f), and radiuses (r) of curvature. The overall length of the lens system is shortened to secure the quantity of light and compensate the coma in accordance with formulas I and III, and the thickness of the first and second lenses is controlled in accordance with formulas II and IV. An overcompensated distortion is generated by the second negative lens to balance the lens system as the whole in accordance with formulas V and VI, and the curvature of stucking between the third and fourth lenses is controlled to compensate the coma of a lower luminous flux in accordance with formulas VII and VIII. Thus, the lens system is made compact to have >=60 deg. field angle, F3.5 brightness, and 1.055-1.085 telephoto ratio, and various aberrations are compensated well.
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