Grades 3–5 · Arts & Music
How does a dark chamber make a picture without a lens?
A camera obscura is a dark chamber with a small opening facing a bright scene. Light from the scene passes through the opening and reaches a screen inside. A small enough opening can produce a recognizable image without a lens.
In the diagramA small aperture selects crossing light pathsobjectpinholescreentop → bottomRepresentative straight paths; no lens and no bending at the hole.
Light from each point of an object travels in many directions. The opening admits only a narrow bundle from each point. Light from the top of the object passes downward through the hole and reaches the bottom of the screen.
Light from the bottom passes upward and reaches the top. The paths cross at the opening without bouncing or turning there. The result is an inverted picture: top and bottom, and left and right, are reversed.
A larger opening admits more light but also allows more overlap between bundles, which can blur the image. A very tiny opening has other limits because light behaves as a wave. The hole selects paths; it does not bend them like a lens.
About this explanation
Starting knowledge: Know that light reflects from objects and travels along approximately straight paths through ordinary air.
Sources
- Exploratorium — Pringles Pinhole: What’s Going On?