Variable focal length objective having four lens groups

Claim 1

Variable focal length objective of high power comprising along an optical axis in the order from the front to the rear a first lens means having positive power of refraction, a second lens means having negative power of refraction, and third and fourth lens means having positive power of refraction; said second negative lens means and said first positive lens means being simultaneously movable along said optical axis so that said second negative lens means substantially effects a variation of the focal length of the objective while said first positive lens means substantially maintains the picture in a constant position, said first lens means including a first lens and a second lens, said second lens means including a third lens, a fourth lens, and a fifth lens, said third lens means including a sixth lens, and said fourth lens means including a seventh lens, an eight lens, a ninth lens, and a tenth lens; said objective having numerical data substantially as set forth in the following table in which the numerical data refer to the mean focal length fM as unit, wherein fM is the geometrical mean of the maximal and minimal focal lengths of the objective, wherein s'' is the focal intercept length, wherein I to IV designate said first to fourth lens means; wherein L1 to L10 designate said first to tenth lenses, wherein r1 to r19 represent the radii of curvature and d1 to d18 represent the apex distances of said lenses along said optical axis, wherein nd represents the indices of refraction for the d-line of the spectrum and Vd represents the Abbe dispersion numbers of said lenses, wherein D1 to D19 are the surface powers of refraction of said lenses; wherein the aperture ratio is 1:9; and wherein fmax and fmin represent the maximal and minimal focal lengths of the objective: