| 摘要 |
PURPOSE:To obtain a zoom lens of high variable magnification ratio with a simplfied structure of the lens barrel and high productivity, by satisfying the prescribed conditions for a 4-group lens system of negative, positive, negative and positive lenses in that order from the side of an object. CONSTITUTION:The 3rd group lens is fixed at a certain distance from an object image surface and at the same time the conditions of inequalitiesI-IV are satisfied for a 4- group zoom lens containing negative, positive, negative and positive lenses in that order from the side of the object. In this case, fT and fW are the maximum and minimum resultant focal distnaces of the whole lens system, fRW is the resultant focal distance of the rear lens component of the fW, PT and PW are the distance from the image side principal point of the 2nd group lens to the object side principal point of the rear lens component for the fT and fW respectively, Smax is the maximum value of the sum S of the distance between the image side principal point of the 2nd group and the object side principal point of the 3rd group and the distance between the principal points of the 3rd and 4th groups, f1 is the focal distance of the 1st group, and L is the distance between the principal points of the 3rd and 4th groups respectively. As a result, the structure of the lens barrel can be simplified with improvement of productivity for a high variable magnification zoom lens. |
