Patent ID: 8331035

Claim:
An image pickup apparatus including a variable power imaging optical system comprising in order from an object side: a first lens group having a positive refractive power; a second lens group having a negative refractive power; a third lens group having a positive refractive power; and a fourth lens group having a negative refractive power, wherein the fourth lens group comprises two lens components namely, a positive meniscus lens having a convex surface directed toward an image side, and a biconcave negative lens in order from the object side, or, one lens component in which, the positive meniscus lens having the convex surface directed toward the image side, and the biconcave negative lens are cemented in order from the object side, and the fourth lens group satisfies the following conditional expressions (1) and (2) N d4 ≦−0.015×ν d4 +2.04 (1) −2.5≦ f G4 /L≦− 1.5 (2) where, N d4 denotes a refractive index of a glass material of the positive meniscus lens in the fourth lens group of the image forming optical system, ν d4 denotes Abbe's number (n d1 −1)/(n F1 −n C1 ) for a d-line of the glass material of the positive meniscus lens in the fourth lens group of the image forming optical system, f G4 denotes a focal length of the fourth lens group in the image forming optical system, L denotes a length of a diagonal of an image pickup element, and n d1 , n C1 , and n F1 denote refractive indices of the positive meniscus lens for the d-line, a C-line, and an F-line respectively.