Задача id13188

The image of the Sun was obtained on the screen using a system of two identical lenses with a focal length F, located at a distance of F/2 from each other. How many times is the illumination of the image of the Sun by rays passing through the lens system greater than the illumination of the screen by direct rays? The angular size of the Sun is equal to a, the diameters of the lenses are equal to D.

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