| 摘要 |
PROBLEM TO BE SOLVED: To provide an image forming optical system that well corrects field curvature stringently required especially in a high variable power ratio and size reduction, while simultaneously achieving size reduction and a high variable power ratio, and also to provide an electronic image pickup apparatus including the same.SOLUTION: In an image forming optical system comprising in order from an object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a positive refractive power, a refractive index for a d-line of a positive single lens L3 having the largest refractive power among all lenses constituting the second lens group is set to be the smallest among refractive indexes of lenses constituting the second lens group. |
