PROBLEM TO BE SOLVED: To generate the image of a panoramic scene on a flat focal plane by generating a small F-number by a visual field angle perpendicular to the output optical axis of an optical assembly. SOLUTION: Energy incoming from the panoramic scene involving the angle of elevation enters an aperture 110, and is reflected by a first element 102, and optical power forms an imaginative pupil 113. The energy is reflected downward by the element 102, and is reflected to the ternary surface of the subelement 42 of a third element by a concave mirror 78. The energy is moved between secondary and ternary surfaces 76 and 42, and passes a visual field diaphragm 112 and the imaginative pupil. A real pupil 146 is relayed to the second surface 148 of a filter and a cold diaphragm 48, and the visual field diaphragm 112 limits the visual field angle of the energy for a route descending from the element 42 to the element 44, and a baffle 74 normally limits incoming radiation deviated from a shaft abutting the surface of an optical element 44. Thus, the small F-number is generated at the visual field angle nearly perpendicular to the output optical axis of the optical assembly on the panoramic scene.