| 摘要 |
PURPOSE:To reduce the influence of eccentricity and an error in assembly with a simple constitution and to correct a spherical aberration excellently by employing two-group, two-element constitution of a positive and a positive meniscus lens and setting specific conditional expressions among the radius of curvature, focal length, and refractive index. CONSTITUTION:This collimator lens consists of the positive lens and positive meniscus lens in two groups from an object side and a specific conditional expression IV holds, where (ri) is the radius of curvature of the (i)th surface from the object side, (fi) is the focal length, and Ni is the refractive index. Expression I and II increase the radius of curvature of the 2nd lens to prevent surface sagging and a coma is prevented from being generated with the lower limit of the expression I; and a back focus is secured with an expression III and when the back focus exceeds its upper limit, it is not within the range between the upper limit of the expression I and the lower limit of the expression II. Deterioration in performance due to eccentricity is prevented and a deficiency in the compensation of the spherical aberration is prevented with the expression IV. Thus, the influence of the eccentricity and error in assembly is reduced with the simple constitution and the aspherical aberration is compensated excellently.
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