| 摘要 |
PURPOSE:To reduce the size and cost of a zoom lens and to improve the imaging performance thereof by forming the lens into 4-groups constitution having positive, negative, positive, and positive refracting powers successively from an object side and executing zooming by fixing the 1st group and 4th group and moving the 2nd group and the 3rd group in the same direction while varying the relative spacings between the 2nd group and the 3rd group. CONSTITUTION:This zoom lens is constituted, successively from the object side, of the 1st group having the positive refracting power, the 2nd group having the negative refracting power, the 3rd group having the positive refracting power, and the 4th group having the positive refracting power. The zooming of this lens is executed by fixing the 1st group and the 4th group and moving the 2nd group and the 3rd group in the same direction along the optical axis while changing the relative spacing in order to correct the fluctuations in variable powers and imaging position. Namely, the 2nd group is divided to 2 pieces of lenses; negative and positive lenses and the spacing between these two parts is slightly changed together with the movement at the time of the variable power of the 2nd group so that the image position is held constant. The need for the conventional 3rd group is thus eliminated. The zoom lens having the good imaging performance with the smaller number of the lenses to be constituted and the shorter overall length is thereby obtd.
|
