Light quantity adjusting device, optical system having the same, and image taking apparatus

摘要

An optical performance is deteriorated by a minute phase difference of transmission wave front of an ND filter. In a light quantity adjusting device which includes an ND filter (P1) for attenuating a quantity of light passing through an aperture formed by diaphragm blades (S11 and S12) and in which a cover ratio of the aperture by the ND filter (P1) is changed, setting is conducted such that a phase difference between lights with a predetermined wavelength lambd which pass through regions (N11, N12, and N13) of the ND filter (P1) with different transmittances inside the aperture becomes substantially 0lambd, substantially 1lambd, or substantially 2lambd in a state in which the aperture is completely covered with the ND filter (P1).