The invention relates to an optical system or apparatus such as a lens system capable of focus control and a variable-focus lens, which has reduced power consumptions, ensures noiseless operation and fast response and contributes to cost reductions for the reason of simplified structure. Specifically, the invention provides an optical apparatus comprising an element 409 having variable optical properties and an image plane 612. To correct the optical apparatus for movement of the image-formation surface of an optical system 614 in association with a change in the element 409 having variable optical properties, the image plane 612 is placed in the range of movement of the image-formation surface in association with the change in the element having variable optical properties.