An optical system for imaging an object on an image acquisition unit includes a first lens unit, a second lens unit, a third lens unit, a fourth lens unit, a fifth lens unit, and a sixth lens unit disposed from the object in the direction of the image acquisition unit. The second lens unit is manufactured from a material whose deviation of the relative partial dispersion fulfills the condition: Δθg F>0.025. The third lens unit is manufactured from a material whose deviation of the relative partial dispersion fulfills the condition: Δθg F