| 摘要 |
PROBLEM TO BE SOLVED: To provide a compact zoom lens that offers a large aperture ratio and good imaging performance over a wide wavelength range of light from the visible range to the near-infrared range.SOLUTION: A zoom lens comprises a first lens group having negative refractive power, an aperture stop STOP, and a second lens group having positive refractive power, and is configured such that a distance between the first and second lens groups changes The second lens group has one or more positive lenses and negative lenses, and a refractive index Ns of a material at a wavelength of 400 nm, refractive index Nm of the material at a wavelength of 1050 nm, refractive index Nl of the material at a wavelength of 1700 nm, and a partial dispersion ratio θ of the material satisfy a relationship expressed as:θ=(Ns-Nm)/(Ns-Nl). An average partial dispersion ratio θIR(G2p)of a material of the positive lenses belonging to the second lens group and an average partial dispersion ratio θIR(G2n)of a material of the negative lenses belonging to the second lens group are each set appropriately.SELECTED DRAWING: Figure 1 |
