| 摘要 |
PURPOSE:To compensate the chromatic aberration of a rear attachment lens to an extent where it has sufficient performance for naked-eye viewing by separating the rear attachment lens of two elements in two groups. CONSTITUTION:The rear attachment lens consists of two elements in two groups, i.e. negative lens having its concave surface on the image side and positive meniscus lens having its convex surface on the object side. Then, inequalities 1-3 hold, where f1 is the focal length of a telescope objective, d1 the fitting gap between the objective and rear conversion lens, r1(r2) the radius of curvature of the object-image side surface of the negative lens in the rear conversion lens, and nu1(nu2) the Abbe number of the negative (positive) lens in the rear conversion lens. When the lower limit of the inequality 1 is exceeded, the size is made large and when the upper limit is exceeded, that is disadvantageous to aberration compensation. When the lower limit of the inequality 2 is exceeded, the spherical aberration is compensated too much and when the inequality 3 does not hold, it becomes difficult to compensate the chromatic aberration on the axis.
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