The present invention provides an optical system for illuminating and viewing a target in which an illumination element and a receiving means are disposed behind a single optical window, and which obtains data essentially free of backscatter and stray light. The optical window of the optical system is configured such that it defines a shape having at least one focal curve, i.e., an ellipsoid shaped dome. The illumination element and the receiving means are geometrically positioned on the focal curve plane or in proximity of the focal curve plane, such that, when illuminating, rays from the illumination elements, that are internally reflected from the optical window, will not be incident on the receiving means.