What do you mean by 4 times and 20 times zoom of mobile phone camera?

The zoom mentioned by mobile phones is mostly digital zoom, which only enlarges the image, and at the same time, it will cause a serious graininess of the picture, which is equivalent to bringing the object 100 meter closer by 4 times to 25 meters. It doesn't make any sense to the quality of photos, and it's basically useless.

The real zoom is optical zoom. By adjusting the distance between the photosensitive original and the lens, the shooting physics is closer visually. Zoom can be divided into digital zoom and optical zoom, generally digital zoom, ranging from 4x to 6x, that is, the magnification is equivalent to moving forward when taking pictures, and the image becomes larger. It is still useful to move backward to make the image smaller, but compared with mobile phones, the pixels are lower.

Optical zoom is achieved by changing the position of lens, object and focus. When the image plane moves in the horizontal direction, as shown below, the visual field and focal length will change, and the farther scenery will become clearer, making people feel that the object is moving forward. ?

Extended data

Most of the optical zoom multiples of mobile phones are between 2 and 5 times, and objects beyond 10 meter can be zoomed to 5-3 meters; There are also some mobile phones whose optical zoom effect is 10 times. The optical zoom factor of home camcorder is 10 ~22 times, and it can clearly shoot things 70 meters away. Using a magnifying glass can increase the optical zoom factor of the camera.

If the optical zoom factor is not enough, you can add a zoom lens in front of the lens. The calculation method is as follows: A 2-fold zoom lens is set on a 4-fold optical zoom digital camera, and then the optical zoom multiple of this digital camera will be changed from the original 1, 2,3,4 times to 2,4,6 times and 8 times, that is, it is obtained by multiplying the zoom lens multiple and the optical zoom multiple.