Patent ID: 6084721
Filing Date: 2000-07-04
Classification: G02B

Abstract:
A zoom lens comprising, in succession from the object side:a first lens unit of positive refractive power fixed during a focal length change;a second lens unit of negative refractive power for focal length change;a third lens unit for correcting the fluctuation of the image plane resulting from the focal length change; anda fixed fourth lens unit of positive refractive power,said second lens unit having a lens subunit of negative refractive power and a lens subunit of positive refractive power, characterized in that said lens subunits are moved at different speeds during the focal length change from the wide angle end to the telephoto end, and when the focal lengths of said negative lens subunit and said positive lens subunit are defined as f2A and f2B, respectively,7.3<.vertline.f2B/f2A.vertline.<27is satisfied, andwhen the focal length of the entire system at the wide angle end is defined as fw and the principal point spacings of the negative lens subunit and the positive lens subunit at the wide angle end and any zoom position are defined as DW and D, respectively, and the zoom ratio is defined as Z, at a zoom position Z0 in at least a portion within the zoom range of a focal length fm (=fw.times.Z.sup.1/2) from the wide angle end, the condition tha tDW<Dis satisfied, andwhen at said zoom position Z0, the sum total of the tertiary spherical aberration coefficients of said positive lens subunit and said third lens unit is defined as Im and the sum total of the tertiary spherical aberration coefficients of said negative lens subunit and said third lens unit, when said negative lens subunit is fixed at said zoom position Z0 and the positional relation of said positive lens subunit relative to said negative lens subunit is a state at the wide angle end and a case where the fluctuation of the image plane is corrected by said third lens unit is prescribed, is defined as Ip, the condition thatIm-Ip<0is satisfied.