(a) Field of the Invention
The present invention relates to a zoom lens system for still cameras with a zoom ratio about 3.
(b) Description of the Prior Art
As zoom lens systems for still cameras, there are known ones disclosed, for example, in Japanese published unexamined patent application No. 131852/78 and Japanese published unexamined patent application No. 42208/81. Out of the above-mentioned known zoom lens systems, the former (Japanese published unexamined patent application No. 131852/78) has a master lens with simple lens configuration. However, its zoom ratio is small, i.e., 2.5, and its aperture ratio is small, i.e., the F number is 4.5. The latter (Japanese published unexamined patent application No. 42208/81) has a zoom ratio about 3. However, its chromatic aberration of spherical aberration in the teleposition is large and, therefore, the contrast of image obtained in the teleposition becomes unfavourable.
In case of zoom lens systems with a zoom ratio about 3 like the latter zoom lens system, chromatic aberration of spherical aberration in the teleposition becomes large. As a result, the contrast decreases and it is comparatively difficult to improve this point.