Patent ID: 9594236
Date: 2017-03-14
CPC Classifications: G02B

Claim:
1. A projection optical system having a zooming function comprising: a plurality of positive lenses and a plurality of negative lenses; and an aperture stop arranged between a negative lens A arranged closest to an enlargement conjugate side out of the plurality of negative lenses and a positive lens C arranged closest to a reduction conjugate side out of the plurality of positive lenses, wherein, when a negative lens arranged at a position closest to the aperture stop, among negative lenses whose lens surfaces are arranged in a range up to a position separated in 0.22 L to the reduction conjugate side from a vertex of a lens surface arranged closest to the enlargement conjugate side both at a wide angle end and at a telephoto end is referred to as a negative lens B when a distance from the vertex of the lens surface arranged closest to the enlargement conjugate side to a vertex of a lens surface arranged closest to the reduction conjugate side is referred to as a total optical length L, when a positive lens arranged at a position closest to the aperture stop, among positive lenses whose lens surfaces are arranged in a range up to a position separated in 0.29 L to the enlargement conjugate side from the vertex of the lens surface arranged closest to the reduction conjugate side both at the wide angle end and at the telephoto end is referred to as a positive lens D, when a refractive index for a d line (wavelength: 587.6 nm) of a material is referred to as Nd, when a refractive index for an F line (wavelength: 486.1 nm) of a material is referred to as NF, when a refractive index for a g line (wavelength: 435.8 nm) of a material is referred to as Ng, when a refractive index for a C line (wavelength: 656.3 nm) of a material is referred to as Nc, when an Abbe number νd, a partial dispersion ratio θgF, and anomalous dispersion ΔθgF are defined as when the Abbe number and the anomalous dispersion of a material for the negative lens A are referred to as νdA and ΔθgFA, respectively, when the Abbe number and the anomalous dispersion of a material for the negative lens B are referred to as νdB and ΔθgFB, respectively, when the Abbe number and the anomalous dispersion of a material for the positive lens C are referred to as νdC and ΔθgFC, respectively, and when the Abbe number and the anomalous dispersion of a material for the positive lens D are referred to as νdD and ΔθgFD, respectively, conditional equations of are satisfied.