Imaging optical system and image projection apparatus

An optical system comprising a plurality of lens groups, the plurality of lens groups each including at least one lens and moving such that spaces between each one of the plurality of lens groups change during a zooming action,

• wherein the optical system conjugates a conjugate point on a magnification side of the optical system and an intermediate imaging position inside the imaging optical system, and conjugates a conjugate point on a reduction side of the optical system and the intermediate imaging position,
• wherein the optical system includes in order from the magnification side toward the reduction side, a first lens group located at a furthest place on the magnification side and a rear group,
• wherein the first lens group includes a field curvature correction lens group including at least one lens element and moving along an optical axis to change an amount of a field curvature of the optical system, and a focusing lens group including at least one lens element and moving along the optical axis during a focusing action from an infinity focus state to closest focus state,
• wherein the optical system satisfies condition (4) below:
• |{(1−βcw2)×βcrw2}/{(1−βfw2)×βfrw2}|<0.2 (4)
• where,
• βcw is a paraxial lateral magnification, at a wide angle end, of the field curvature correction lens group moving along the optical axis to change the amount of the field curvature,
• βcrw is a paraxial lateral magnification, at the wide angle end, of every lens located farther on the reduction side than the field curvature correction lens group moving along the optical axis to change the amount of the field curvature,
• βfw is a paraxial lateral magnification, at the wide angle end, of the focusing lens group moving along the optical axis during the focusing action, and
• βfrw is a paraxial lateral magnification, at the wide angle end, of every lens located farther on the reduction side than the focusing lens group moving along the optical axis during the focusing action.