| 摘要 |
PURPOSE:To improve the accuracy in detecting focus in a method for detecting focus by a secondary imaging system, by correcting the aberration of a reimaging lens thereby improving the optical performance of the reimaging on a photodetector surface. CONSTITUTION:A reimaging lens is constituted of the 1st and the 3rd lenses consisting of a biconvex lens and the 2nd lens consisting of a biconcave lens. The nu+ value of the medium for the positive lens and the nu- value of the medium for the negative lens are set at nu+>nu- in order to correct a chromatic aberration. If Ri is defined as the radius of curvature of the ith lens face from the object side, it is set at R1<¦R2¦, R5>¦R6¦ in order to correct a spherical aberration. It is also possible to make the one lens aspherical in order to provide a better correction. |
