of the fixed 3rd lens group iii it is preferred that the following conditions be satisfied of these conditions condition 2 is for realizing a mode of movement in view of the prerequisite that the 2nd lens group ii be moved along a camming slot of gentle slope and conditions 3 and 4 are to compensate for the deterioration of aberrations produced when the power distribution over the 3rd lens group iii which remains stationary during zooming thus contributing to a good stability of aberration correction of the entire system the upper limit of condition 2 represents a minimum ratio of the total movements of the 1st lens group i and the 2nd lens group ii which permits gentle slop of the camming slot for the 2nd lens group to assure smooth zooming operation when the upper limit is exceeded though it is advantageous at aberration correction the telephoto ratio is objectionably increased with increase in the total optical length on the other hand when the lower limit is exceeded the petzval sum increases to the negative direction over correction of field curvature results astigmatism also increases and at the same time zonal spherical aberration too increases condition 4 is to shorten the total length of the lens within the framework of condition 3 since in the embodiments the lens takes a longer total length when in telephoto settings the ratio of the length of the 3rd lens group iii to the total length of the lens in the wide angle setting is large as compared with the ordinary zoom lenses when the upper limit is exceeded the total length of the lens is elongated to involve an increase in the diameter of the front lens members.