Patent ID: 6549343
Filing Date: 2003-04-15
Classification: G02B

Abstract:
An intermediate telephoto lens system comprising a positive first lens group, and a positive second lens group, in this order from an object;wherein said first lens group comprises a positive first lens element having stronger positive power on the object-side surface thereof, a positive second lens element comprising a positive meniscus lens element having positive power on the object-side surface thereof, a negative third lens element comprising a negative meniscus lens element having the concave surface facing toward an image, an aperture stop, cemented lens elements comprising a negative fourth lens element having a concave surface facing toward said object and a positive fifth lens element, and a positive sixth lens element, in this order from said object; wherein said second lens group comprises a negative seventh lens element comprising a negative meniscus lens element having the convex surface facing toward said object, and a positive eighth lens element, in this order from said object; wherein upon focusing, only said first lens group moves along the optical axis; and wherein said intermediate telephoto lens system satisfies the following condition: (&ngr;â€²1-1+&ngr;â€²1-2)/2>102 wherein &ngr;â€²1-1 designates the dispersion ratio of said positive first lens element; &ngr;â€²1-2 designates the dispersion ratio of said positive second lens element; (&ngr;â€²=(ndâˆ’1)/(ngâˆ’nF) nd designates the refractive index of the d-line with respect to each lens element; ng designates the refractive index of the g-line with respect to each lens element; and nF designates the refractive index of the F-line with respect to each lens element.