An apparatus for improving contrast in an image captured by an imaging sensor. The apparatus including: an objective optical system positioned in an optical path of illumination light on an object; an image sensor positioned in the optical path such that light from the objective optical system is incident on the image sensor; a device having a variable transparency positioned at a focal plane of the objective optical system; and a processor configured to: detect a bright spot on the image sensor; and control the device to change a transparency of a portion of the device corresponding to the detected bright spot.