The invention relates to an image-formation lens system well balanced among cost
reductions, size reductions and performance improvements and an imaging system
incorporating that lens system. The image-formation lens system in the imaging
system is a zoom lens system that comprises at least three lens groups including
a first lens group G1 of positive power, a second lens group G2 of
positive power and a third lens group G3 of negative power, wherein zooming
is carried out by varying the spacing between adjacent lens groups. The zoom lens
system comprises a total of up to 8 lenses, and satisfies the following conditions:
0.07g/IH0.23 (1)
1.8TeleFno/WideFno3 (2)
-8%DTLw8% (3)
Here g is a difference between the rear focal positions at
d- and g-lines of the zoom lens system at the telephoto end, IH is the maximum
image height at the image plane, WideFno and TeleFno are the F-numbers at d-line
of the zoom lens system at wide-angle end and telephoto end, respectively, and
DTLW is an amount of d-line distortion at an angle of view of 28.0
at the wide-angle end.
