How to build an image of a point source: a) in a collecting lens; b) a diffusing lens?

a) It is necessary to construct two rays from the source. The first, parallel to the main optical axis of the lens, after refraction in the lens, the beam will pass through the main focus of the lens. The second ray through the optical center of the lens, it will pass through the lens without refraction. The point of intersection of the ceased rays – the image of the source in the lens b) From the source it is necessary to construct two rays. The first, parallel to the main optical axis of the lens, after refraction in the lens, the ray will go in such a way that its continuation passes through the main focus of the lens. The second ray through the optical center of the lens, it will pass through the lens without refraction. The intersection point of these rays is the source image in the lens.

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