1. Field of the Invention
This invention relates to zoom lenses and, more particularly, 3-component zoom lenses of extended range to about 3, while still maintaining minimization of the size and weight of the entire lens system to be achieved, suited to photographic cameras or video cameras.
2. Description of the Related Art
Of the zoom lenses of relatively high ratio of focal length variation which have found their use in photographic cameras, video cameras, etc., there is a type in which the total number of lens groups is four, or the so-called 4-component zoom lens. This zoom lens comprises, from front to rear, a first lens group of positive power for focusing, a second lens group of negative power monotonously movable for mainly varying the image magnification, a third lens group of negative or positive power non-linearly movable for compensating for the shift of an image plane resulting from the variation of the image magnification, and a fourth lens group of positive power having an image forming function.
The 4-component zoom lens of this character, while being corrected for the variation of aberrations with zooming by the first to third lens groups, has its fourth lens group made to correct the zooming-independent aberrations, or so-called bias component aberrations.
For this reason, the structure of the constituent members of the fourth lens group tends to get relatively complicated. This leads to a problem that the physical length of the lens becomes long.
Another problem arises from the arrangement of the stop in between the third lens group and the fourth lens group. Because of the long distance from the first lens group to the stop, to admit of the off-axial light beam, the diameter of the first lens group has to increase.
Meanwhile, Japanese Patent Publication No. Sho 58-32684 discloses a zoom lens of relatively small size comprising, from front to rear, a first lens group of positive power, a second lens group of negative power and a third lens group of positive power, these three lens groups being moved to effect variation of the focal length.
The zoom lens proposed in the same document has its range of image magnification limited to 2.5 or thereabout. Also, because the zooming movement of the first lens group is made to be directed to the object side, the diameter of the first lens group and the total length of the entire lens system tend to increase in any way.
USPTO Backgrounds
USPTO Backgrounds