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.

 
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