Video narration
How can a box make a picture without a lens? Your smartphone uses a lens; a pinhole camera uses a hole and screen. Light travels in straight lines: rays from each point cross at the hole and form an upside-down image on the screen. Move the screen back: the image grows, increasing magnification. Move it closer: it shrinks. A larger hole is brighter, but overlap blurs it. A smaller hole reduces overlap and sharpens the image, while letting in less light. But smallest is not best. Make it extremely tiny, and diffraction-light spreading at the edge-blurs the image again. With several holes, images overlap; a grid makes the result brighter but less clear. So every pinhole camera-also called a camera obscura-trades brightness, sharpness, image size, and overlap. That is how a box makes a picture without a lens: one tiny hole sorts straight-line rays.