Abstract: In a method for designing a mirror, a design formula of a reflecting surface is used which is derived based on conditions that: an intersection point between a sagittal light source ray and an incoming light ray to an MA point and an intersection point between a meridional light source ray and the incoming light ray to the MA point are represented by using L1sA and L1mA, respectively; an intersection point between an outgoing light ray from the MA point and a sagittal virtual collected light ray and an intersection point between the outgoing light ray from the MA point and a meridional virtual collected light ray are expressed by using L2sA and L2mA; an intersection point between a sagittal virtual light source ray and an incoming light ray to an MB point and an intersection point between a meridional virtual light source ray and the incoming light ray to the MB point are expressed by using L2sA and L2mA, and L; and an intersection point between an outgoing light ray from the MB point and the sagittal collect

Abstract: In a method for designing a mirror when any point on a reflecting surface is represented by M, coordinates of an intersection point between a sagittal light source ray and an incoming light ray to the M point and an intersection point between a meridional light source ray and the incoming light ray to the M point are expressed by using L1s and L1m, and coordinates of an intersection point between an outgoing light ray from the M point and a sagittal collected light ray and an intersection point between the outgoing light ray from the M point and a meridional collected light ray are expressed by using L2s and L2m. A mirror is designed using design formulas of a reflecting surface derived based on the coordinates and a condition that an optical path length from a light source position to a light collection position is constant with respect to any point on the reflecting surface for both the light collection in the sagittal direction and the light collection in the meridional direction.