What is the principle of pinhole imaging?

Principle: straight line propagation of light

The linear propagation of light refers to the linear propagation of light in the same uniform medium, which is an important basis of geometric optics and can be used to solve the imaging problem concisely.

Blocking a plate with a small hole between a wall and an object will form the reflection of the object on the wall. We call this phenomenon pinhole imaging. Moving the middle board back and forth will change the size of the image on the wall, which shows the nature of light propagating along a straight line.

A small hole was opened in the Chaoyang wall of a dark hut. People stood outside the house facing the hole, and an inverted figure appeared on the wall opposite the room.

Like archery, light travels in a straight line through a small hole. A person's head covers the light above, and his feet cover the light below, forming a reflection. This is the first scientific explanation for the straight-line propagation of light.

Extended data

Property application

1, ancient astronomical calendar

The linear propagation of light has been widely used in ancient astronomical calendars in China. Our ancestors made standard watches and sundials and measured the length and direction of shadows to determine the time, winter solstice and summer solstice. Install peepholes on astronomical instruments to observe the sky and measure the positions of stars.

In addition, our country has long used this characteristic of light to invent shadow play. In the early Han Dynasty, people and things cut by Qi Shaoweng were performed behind a white screen, and the images of people and things were reflected on the white screen with light, so people outside the screen could see the performance of the images. Shadow play was very popular in the Song Dynasty, and later spread to the West, causing a sensation.

2. Cameras and camcorders

Nowadays, some cameras and video cameras use the principle of pinhole imaging-the lens is a pinhole (most of them are equipped with convex lenses to ensure the imaging distance of light), and the scene enters the darkroom through the pinhole, as if it were left on the film by some special chemicals (such as developer). ).

Wave theory of light

It plays a key role in the wave theory of light, such as Young's interference experiment and double-slit experiment. The principle of pinhole imaging and the method of interference experiment are still very useful in modern physics.

Reference Baidu Encyclopedia-Pinhole Imaging