Patent ID: 7580199

Claim:
A zoom lens comprising: a focus unit including a focus lens unit; a zoom unit including a zoom lens unit; an aperture stop configured to adjust a light quantity; and an imaging unit including a lens unit that does not move for zooming and a splitting element, wherein the focus unit, the zoom unit, the aperture stop, and the imaging unit are arranged in that order from an object side to an image side, wherein the splitting element includes: an incident surface on which a light beam from the aperture stop is incident; a half mirror surface configured to split the light beam from the incident surface into reflected light and transmitted light; a splitting exit surface from which the reflected light from the half mirror surface is emitted after being reflected by a part of the incident surface; and an exit surface from which the transmitted light passing through the half mirror surface is emitted, wherein the incident surface and the exit surface are perpendicular to an optical axis of the zoom lens, and wherein the following conditions are satisfied: 0.1 < ⅆ P ⅆ T < 0.4 ( 1 ) 0.25 < D C D B < 0.77 ( 2 ) where d P represents a distance from the aperture stop to the exit surface of the splitting element, d T represents an equivalent air length from the aperture stop to an image plane of the entire zoom lens, D B represents an effective diameter of the exit surface of the splitting element, and D C represents an effective diameter of the splitting exit surface of the splitting element.