PURPOSE: To increase the zooming ratio, viewing angle and aperture ratio in spite of being a small lens by specifying the refractive power of each lens group so as to satisfy a specified conditional expression.
CONSTITUTION: This zoom lens is provided, in order from the object side, with a first lens group G1 having positive refractive power and fixed to a reference image position, a second lens group G2 having negative refractive power and power varying action by moving on the optical axis, an aperture diaphragm, a third lens group G3 fixed to a reference image position and having light converging action and positive refractive power, and a fourth lens group G4 moving on the optical axis so that an image plane fluctuated by the movement of the second lens group G2 and the object is held at a fixed position from the reference image position and having positive refractive power. By representing the focal distance of ith lens group by fi (i=1 to 4), the distance from the final surface of a lens to the image plane when the image space is filled with air by BF and the focal distances of the third lens group G3 for d line, c line and F line of spectrum by f3d, f3c and f3F, respectively, the expressions are satisfied.
OKAYAMA HIROAKI
ONO SHUSUKE
II TOSHIYUKI
