| 摘要 |
PURPOSE:To improve aberration compensation, by employing four-group, four- element constitution including a convex, a biconcave, and a concave lens, and the 4th positive lens successively from an object side, arranging an aperture behind the 4th lens, and satisfying specific condition inequalitites. CONSTITUTION:This lens system has the four-group, four-element constitution, namely, consists of the positive meniscus lens L1 having a convex surface on the object side, biconcave lens L2, positive meniscus lens L3 having a convex surface on the image side, and positive lens L4, and the aperture is arranged behind the 4th lens. Then, a condition inequality (1) is for compensating aberrations within a 50 to 61 deg. angle-of-view range, and condition inequalities (2) and (3) are for preventing a decrease in the quantity of ambient light, where N1 and N4 are refractive indexes of the lenses L1 and L14, d1 and d7 are on-axis core thicknesses, and SIGMAd the overall length of the lens system. Consequently, the aberrations of the lens system of aperture-behind constitution which has about F2.8 and a 50-61 deg. angle of view are compensated excellently. |
