Patent ID: 8593735

Claim:
An image forming optical system comprising four or five lens groups in total including, in order from its object side to image side, a first lens group having a positive refracting power, a second lens group having a negative refracting power, a third lens group having a positive refracting power, and a fourth lens group having a refracting power, wherein during zooming from the wide angle end to the telephoto end, the distance between the first lens group and the second lens group increases, the distance between the second lens group and the third lens group decreases, and the distance between the third lens group and the fourth lens group changes, the first lens group comprises three lenses including a negative meniscus lens, a positive meniscus lens, and a positive lens, the second lens group includes a negative meniscus lens having a convex surface directed toward the object side and a concave surface directed toward the image side, the negative meniscus lens being located closest to the object side in the second lens group, the position of the second lens group at the telephoto end is closer to the object side than that at the wide angle end, the image forming optical system has an aperture stop that moves integrally with the third lens group, the third lens group includes a positive lens component and a negative lens component, and the fourth lens group consists of one lens.