| 摘要 |
PURPOSE:To maintain superior image-formation performance even when titled rear conversion lens is mounted on an objective with a large aperture ratio by providing the 1st lens group with positive refracting power, the 2nd group with negative refracting power, and the 3rd group with positive refracting power from the object side, and satisfying specific conditional inequalities regarding air gaps between the lens groups. CONSTITUTION:The constitution of the 1st group G1 with positive refracting power, the 2nd group G2 with negative refracting power, and the 3rd group G3 with positive refracting power from the object side is provided on the image side of an F1.4 modified Gaussian type objective, and air gaps D1 and D2 between the 2nd group, and the 1st and the 3rd groups satisfy a condition inequality I for a larger aperture ratio. Then, an inward and an outward comma aberration are compensated by the inequality I . Further, a spherical aberration and an astigmatism are compensated by an inequality II; and the astigmatism and astigmatic difference are compensated by the lower limit of an inequality III and a back focus is securely by the upper limit. A positive and a negative astigmatism are compensated by an inequality IV. Thus, the superior image formation performance is maintained even when the conversion lens is mounted on an objective which has relatively high magnification and a large aperture ratio. |
