To provide an inspection system and a method with the use of a wide-angle optical system.

An optical system includes a wide-angle input lens group and an output lens group. The wide-angle input lens group receives wide-angle emission having an angle spread of, for example, more than 60 degrees from an object surface and generates emission capable of forming an image. The wide-angle input lens group prevents an intermediate focusing image from being formed within the wide-angle input lens group or thereafter. The output lens group receives emission capable of forming an image from the wide-angle input lens group and forms an image of at least a part of the object surface by focusing the emission capable of forming an image onto an image surface. A detector receives the image of at least a part of the object surface and detects, for example, a stain on the object surface on the basis of the received image.