The observer stands with his back to a distant bright source of light and holds at arm's length a flat-convex thin lens, with the flat side facing the eye. He sees two images of the source, one of which is reversed and reduced. By turning the lens with its convex side towards the eye, without changing the distance to it, the observer notices that the reverse image is shifted. Explain the origin of the images. Find the amount of displacement of the inverse image. The focal length of the lens is F = 30 cm, the radius of curvature of its convex surface is R = 16 cm.

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