Zoom lens having small distortion

DETAILED DESCRIPTION The lens system according to the present invention provides a miniaturized zoom lens having small distortion and the other various aberrations to be well compensated, by arranging a third lens group having a negative focal length after a second lens group of a conventional two-group zoom lens whereby the rear lens group of the invention is composed of the second lens group and the additional third lens group which is fixed with respect to the third lens group.
According to the invention, distortion is well compensated for without the variation of the space between the second and third lens groups.
In the invention, distortion is already compensated for between the first and second lens groups and maintained at a small level.
Spherical aberration, coma aberration, astigmatism, field curvature aberration and the like which are generated due to such compensation are well compensated for by the third lens group.
As a result, a zoom lens having small overall distortion is obtained.
Barrel distortion is markedly generated between the first and second lens groups on the short focal length side and the compensation of distortion is enhanced better on the short focal length side than on the long focal length side by great lens power of the third lens group whereby spinning pin cushion distortion is compensated to be small at the long focal length end and at the same time barrel distortion is compensated for to be small at the short focal length end.
It is known that a conventional two-group type zoom lens is available for a wide angle lens but is not available for a telephoto lens.
However, the invention widens the application range of a two-lens group zoom lens to a telephoto lens by use of the additional lens group to the rear lens group.