How to make a pinhole camera

Find an empty matchbox, open a small window on the wide side and stick a piece of translucent paper. Punch a small hole in its back with a needle. After dark, put a lighted candle near the pinhole. You will see the reflection of the candle in the small window.

You can also do this experiment with an old jar (or a square paper box). Cover one end of the opening of the can with a translucent plastic sheet and fix it with a rubber band. Use a small nail to make a small hole (diameter 1 mm to 3mm) in the bottom of the jar. Aim the hole in the jar at a bright room or street. Cover your head with a blanket or a thick coat between cans. You will see a colorful film-like picture on the plastic sheet, but it is upside down.

With such a device, a negative is installed, which is a pinhole camera. Pinholes are equivalent to the lens of a camera. Because the amount of light entering the pinhole is small and the exposure time is long, it cannot be used to shoot moving objects. But it also has its own advantages: because there is no lens, there is no need to focus when taking pictures, and the far and near scenery can be taken clearly, and the viewing angle is larger than that of ordinary cameras. When shooting large buildings, the effect is better than some cameras!

When making a pinhole camera, the pinhole size can refer to the following formula:

D is the distance from the pinhole to the photosensitive plate.

In order to take better photos, we can take more photos with different exposure times and find out the most suitable exposure time, so as to take satisfactory photos.

Images of small holes can often be observed in nature. When the bright sunshine shines obliquely on the ground through the dense leaves, you will see many swaying spots on the ground. Interestingly, no matter what the shape of the holes interwoven with leaves is, every spot is round. Why? It turns out that this is an image of the sun passing through a small hole. The sun is a sphere, so its image is always round. If a partial solar eclipse occurs one day and a part of the sun is missing, many strange crescent spots will be formed.

The characteristic of light propagation along a straight line has many uses in life and production. We all know that plumb line is essential in building engineering, and the master will use it to prevent the wall from being crooked. However, the use of plumb lines sometimes has disadvantages. For example, to install the elevator of Beijing Hotel, in order to install the elevator upright, it is necessary to tie a vertical line from the top of the building more than 80 meters high. In construction, plumb lines are often broken, which affects the progress of the project. Later, the technicians replaced the plumb line with laser, and the progress of the project was faster, because the beam kept hitting and the collision was not bad. When digging a cave tunnel, it is also necessary to rely on the guidance of light beams to straighten the tunnel.