Patent ID: 7180659

Claim:
A cassegrain-type multifield optical combination having an image focal plane, comprising: a first holed concave primary mirror that is fixed relative to the image focal plane and a convex secondary mirror, the structure and the position, in narrow-field configuration, of the mirrors being such that the light that emanates from an external scene considered as being located at infinity and is intended to be focused in the image focal plane is meanwhile reflected firstly by the first primary mirror and then by the secondary mirror, which also includes a second holed concave primary mirror that can move relative to the image focal plane, the structure and the position, in medium-field configuration, since the medium field is wider than the narrow field, of the mirrors being such that the light that emanates from an external scene considered as being located at infinity and is intended to be focused in the image focal plane is meanwhile reflected firstly by the second primary mirror and then by the secondary mirror, wherein the secondary mirror can move relative to the image focal plane, a wide-field focusing optic (WFFO) having a focal length smaller than a distance between the second holed concave primary mirror and the image focal plane that can move relative to the image focal plane simultaneously with said secondary mirror, the structure and the position, in wide-field configuration, since the wide field is larger than the medium field, of the mirrors and of the wide-field focusing optic being such that the light that emanates from an external scene considered as being located at infinity and is intended to be focused in the image focal plane by means of the wide-field focusing optic is not meanwhile reflected by any of said primary or secondary mirrors.