Illuminating method and illuminating device

An illuminating device comprising an optical system for forming an image of an object to be illuminated in which a light beam emitted from N (N is an integer not less than 1) light sources is divided into M divided light beams (M is an integer not less than 2), a light path length difference of not less than a coherent distance is given to the light beams after division, and then, light axes of these light beams are again aligned with each other to illuminate said object with the light beam of coherence reduced by this,

• wherein when the light path length difference from one point on said object to be illuminated to an image corresponding thereto has a standard deviation σZ, the number M and the number N are set so that a relation expressed by the following expression A is satisfied:
• ( numerical ⁢ ⁢ expression ⁢ ⁢ 4 ) ⁢ ⁢ NM · 1 + ( 2 · W · σ z ) 2 4 ≥ 1 Expression ⁢ ⁢ A
• where, “W” indicates a spectrum width of wave number of the light beam emitted from said light source.

An illuminating method using an optical system for forming an image of an object to be illuminated in which after light axes of light beams emitted from N′ (N′ is an integer of 2 or more) light sources are aligned with each other, coherence of the light beams is reduced, and said object to be illuminated is illuminated with the light beams of coherence reduced by this,

• wherein when a light path length difference from one point on said object to be illuminated to an image corresponding thereto has a standard deviation σZ, the number N′ is set so that a relation expressed by the following expression D is satisfied:
• ( numerical ⁢ ⁢ expression ⁢ ⁢ 7 ) ⁢ ⁢ N ′ · 1 + ( 2 · W · σ z ) 2 4 ≥ 2. Expression ⁢ ⁢ D ′
• where, “W” indicates a spectrum width of wave number of the light beam emitted from said light source.

An illuminating device comprising an optical system for forming an image of an object to be illuminated in which after light axes of light beams emitted from N′ (N′ is an integer of 2 or more) light sources are aligned with each other, coherence of the light beams is reduced, and said object to be illuminated is illuminated with the light beams of coherence reduced by this,

• wherein when a light path length difference from one point on said object to be illuminated to an image corresponding thereto has a standard deviation σZ, the number N′ is set so that a relation expressed by the following expression D is satisfied:
• ( numerical ⁢ ⁢ expression ⁢ ⁢ 10 ) ⁢ ⁢ N ′ · 1 + ( 2 · W · σ z ) 2 4 ≥ 1 Expression ⁢ ⁢ D
• where, “W” indicates a spectrum width of wave number of the light beam emitted from said light source.