The sun's rays pass through a circular hole in the opaque screen and illuminate the white screen behind it. Hole diameter d = 20 mm. At what distance L should the white screen be placed so that the illumination at its center is three times less than the illumination created by the rays in the plane of the hole? It is known that a lens with a focal length F = 2 m produces an image of the Sun with a diameter D = 17.4 mm.

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