| 摘要 |
PURPOSE:To increae a veriable power ratio and to shorten the overall length by setting the specific condition equations between a focal length and radius of curvature in the constitution of a front group having a positive refracting power and rear group having a negative refracting power. CONSTITUTION:The front group is constituted, successively from an object side, of positive, negative and positive lenses and a negative meniscus lens of which the concave face is directed to the object side and the rear group is constituted of positive and negative lenses. The conditions equation IV is set between teh focal length (f) and the radius (r) of curvature. The equations, I, II define the focal length of the front and rear groups. The overall length of the lens system increases when the power is weakened by the excess of the upper limits thereof and aberrations are exessive when lower limits are exceeded. The equation III defines the focal length of the negative lens on the image side of the front group. Petzval sum shifts negative when the lower limit is exceeded. The equation IV defines the radius of curvature of the negative lens of the front group and improves the correction of various aberrations. The overall length is, therefore, shortened while the variable power ratio is increased.
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