A device for receiving beams propagating from each of object points (Xa, Xb, Xc) on a surface of an object, comprising an optical unit located to be faced to an offset concaved mirror (2, 2a, 2b, 2c) which allows a local radius of curvature to vary with any location or orientation on a surface of the offset concaved mirror (2, 2a, 2b, 2c); the optical unit is configured to: comprise at least one lens (3a, 3b, 3c); conform a first optical path associated with a first ray to a second optical path associated with a second ray to determine a direction of a chief ray propagating toward the offset concaved mirror (2, 2a, 2b, 2c) from the each of object points (Xa, Xb, Xc), characterized in that the first ray passes a center of entrance pupil of the lens (3a, 3b, 3c) as a chief ray after beams propagated from any object points (Xa, Xb, Xc) on the object surface is reflected by the offset concaved mirror (2, 2a, 2b, 2c), and the first optical path is a segmented path of the first ray from a reflection point on a surface of the offset concaved mirror (2, 2a, 2b, 2c) to the entrance pupil of the lens (3a, 3b, 3c), in that the second ray is included in a beam propagated from a conjugated point corresponding to the center of entrance pupil, and the second optical path is a path from the reflection point to the entrance pupil of the lens (3a, 3b, 3c) when the beam propagated from the conjugated point is reflected by the offset concaved mirror (2, 2a, 2b, 2c) according to a local radius of curvature at the reflection point, and in that the diameter of the entrance pupil is arranged to allow the relating marginal rays of the chief rays to pass through the entrance pupil, and the object is disposed where the conjugate point for an imaging point of the lens (3a, 3b, 3c) associated with the each chief ray corresponds to each object point (Xa, Xb, Xc) on a surface of the object. comprise at least one lens (3a, 3b, 3c); conform a first optical path associated with a first ray to a second optical path associated with a second ray to determine a direction of a chief ray propagating toward the offset concaved mirror (2, 2a, 2b, 2c) from the each of object points (Xa, Xb, Xc), characterized in that the first ray passes a center of entrance pupil of the lens (3a, 3b, 3c) as a chief ray after beams propagated from any object points (Xa, Xb, Xc) on the object surface is reflected by the offset concaved mirror (2, 2a, 2b, 2c), and the first optical path is a segmented path of the first ray from a reflection point on a surface of the offset concaved mirror (2, 2a, 2b, 2c) to the entrance pupil of the lens (3a, 3b, 3c), in that the second ray is included in a beam propagated from a conjugated point corresponding to the center of entrance pupil, and the second optical path is a path from the reflection point to the entrance pupil of the lens (3a, 3b, 3c) when the beam propagated from the conjugated point is reflected by the offset concaved mirror (2, 2a, 2b, 2c) according to a local radius of curvature at the reflection point, and in that the diameter of the entrance pupil is arranged to allow the relating marginal rays of the chief rays to pass through the entrance pupil, and the object is disposed where the conjugate point for an imaging point of the lens (3a, 3b, 3c) associated with the each chief ray corresponds to each object point (Xa, Xb, Xc) on a surface of the object. characterized in that the first ray passes a center of entrance pupil of the lens (3a, 3b, 3c) as a chief ray after beams propagated from any object points (Xa, Xb, Xc) on the object surface is reflected by the offset concaved mirror (2, 2a, 2b, 2c), and the first optical path is a segmented path of the first ray from a reflection point on a surface of the offset concaved mirror (2, 2a, 2b, 2c) to the entrance pupil of the lens (3a, 3b, 3c), in that the second ray is included in a beam propagated from a conjugated point corresponding to the center of entrance pupil, and the second optical path is a path from the reflection point to the entrance pupil of the lens (3a, 3b, 3c) when the beam propagated from the conjugated point is reflected by the offset concaved mirror (2, 2a, 2b, 2c) according to a local radius of curvature at the reflection point, and in that the diameter of the entrance pupil is arranged to allow the relating marginal rays of the chief rays to pass through the entrance pupil, and the object is disposed where the conjugate point for an imaging point of the lens (3a, 3b, 3c) associated with the each chief ray corresponds to each object point (Xa, Xb, Xc) on a surface of the object.