A parallel beam of light illuminates an object. On the screen, there is an image of his shadow obtained by a lens. If frosted glass is placed between the object and the lens, close to the object, then the image on the screen is the same. If we move the frosted glass closer to the lens, the image gradually blurs and disappears. How do you explain this phenomenon?
The image appearing on the frosted glass becomes the object for the lens. By moving the frosted glass we are moving the object. As the object is moved closer to the lens, the image size increases and moves farther away from the lens. Thereby, the image on the screen goes “out of focus.”