What is the reason why mobile phones do not need to adjust the focus when shooting objects at different distances?

Firstly, because the focal length of the general mobile phone lens is small, the object distance is much greater than 2 times the focal length, the image distance is close to the focal length, and the range of image distance change is small, so that the imaging positions of objects at different distances are not much different. So no adjustment is required.

Secondly, because all mobile phones now have autofocus function, manual focus is not required.

Extended information:

Various focusing methods:

1. Autofocus:

Traditional cameras adopt a method similar to visual inspection. The camera emits a kind of infrared ray (or other ray), determines the distance of the subject based on the reflection of the subject, and then adjusts the lens combination based on the measured results to achieve autofocus.

This autofocus method is direct, fast, easy to implement, and low cost, but sometimes errors occur (autofocus cannot be achieved when there are other things between the camera and the subject, such as glass, Or when the light is insufficient), the accuracy is also poor. Nowadays, high-end cameras generally do not use this method. Because the camera actively emits rays, it is called the active type. And because it actually only measures distance and does not judge whether the focus is correct through the actual imaging of the lens, it is also called the non-TTL type.

Compared with active autofocus, this focusing method later developed passive autofocus, which is to judge whether the focus is correct based on the actual imaging of the lens. The basis for judgment is generally contrast detection, and the specific principle is quite complicated. . Because this method is achieved through lens imaging, it is called TTL autofocus. It is precisely because this autofocus method is based on lens imaging that it has high focusing accuracy and a low error rate. However, it is technically complex, slow (except for advanced autofocus lenses using ultrasonic motors), and the cost is high.

2. Manual focus:

Manual focus is a focusing method that adjusts the camera lens by manually turning the focus ring to make the photos taken clear. This method is very convenient. To a large extent, it depends on the human eye's judgment of the image on the focusing screen and the photographer's proficiency and even the photographer's vision. Early SLR cameras and rangefinder cameras basically used manual focus to complete the focusing operation. Today's semi-professional and professional digital cameras, as well as SLR digital cameras, all have manual focus functions to meet different shooting needs.

3. Multi-focus:

Many digital cameras have multi-point focusing function or area focusing function. When the focus center is not set at the center of the picture, you can use multi-point focus, or multiple focus. In addition to setting the position of the focus point, you can also set the focus range, so that users can take pictures with different effects. Common multi-point focusing is 5-point, 7-point and 9-point focusing.

4. Hologram autofocus:

Hologram AF is a unique feature of Sony digital cameras. It is also a brand-new autofocus optical system that uses advanced lasers. Holographic photography technology uses laser points to detect the edges of the subject. It can take accurately focused photos even in dark environments. The effective shooting distance is up to 4.5 meters.