Optical system, inspection system, lithographic apparatus and manufacturing method

Systems and methods for inspection are provided utilizing a wide angle optical system. The optical system includes a wide angle input lens group and an output lens group. The wide angle input lens group is configured to receive wide-angle radiation, e.g., having an angular spread of 60 degrees or more, from an object surface, and produce imageable radiation. The wide angle input lens group is arranged such that no intermediate focused image is formed within or after the wide angle input lens group. The output lens group is configured to receive the imageable radiation from the wide angle input lens group and focus the imageable radiation onto an image plane to image at least part of the object surface. A detector receives the image of the at least part of the object surface and, based on the received image, detects, for example, contamination on the object surface.