Put a sharp and thin pencil and tie a small hole in the center of a piece of hard paper.

The diameter of the hole is about 3mm. Try to stand it upright on the table, and then close the curtains to darken the light in the room.

Light a candle and put it near the hole. Take a piece of white paper and put it on the other side of the hole. In this way, you will see an inverted candle flame on the white paper. We call it the image of a candle. Move the white paper back and forth to see how the candle flame changes. When the white paper is close to the candle, it looks small and bright; When the white paper is slowly away from the candle, the image becomes larger and the brightness becomes darker.

Changing the size of the small hole, let's observe the changes of the image of the candle.

You can tie several holes of different sizes and shapes on the hard paper, and the distance between the holes is a few centimeters. At this time, several inverted images corresponding to the small holes appeared on the white paper. They are all the same size, but the clarity is different. The larger the hole, the less clear the image. As long as the hole is small enough, its shape, whether square, round or flat, has no effect on the clarity and shape of the image.