Mobile phones sometimes have that vague background. What happened?

Follow-up photography can be used when shooting moving objects. The characteristic of follow-up photography is that the photographer should rotate the camera with the moving direction of the moving object and press the shutter when moving. The result is that the moving object is clear and the background is blurred, giving people a feeling of fast movement. Keep the camera close to the face and rotate the camera and head as a whole. When shooting, first look at the position of the subject from the frame. Rotate the camera accordingly and press the shutter in time when the right time comes. 2. When you press the shutter, the camera can't stop, and you must press the shutter while rotating. 3. Don't use too high shutter speed, generally use1/60s, sometimes use1125s or1/30s. That one. If the shutter speed is too slow, it is not easy to master technically, and the subject is easy to blur. 4. When shooting with the follow-up method, it is generally better to choose metering or backlight. You should choose a dark background, preferably with trees, mountains, houses or people. In this way, when you turn the camera, fuzzy lines will appear in the background. If there is no scene or the background is dark, there will be no blurring effect even if the camera is turned when shooting. 5. Follow-up photography is mainly used to express the "dynamics" and "speed" of a moving body. There are the following methods: ① Follow in parallel. When shooting, the camera follows the moving object in parallel. ② Follow vertically. When the mobile body moves longitudinally, the camera follows along the longitudinal direction. For example, if the child swings up, the camera rotates up. ③ Arc following. When a moving object moves along an arc. Arc pursuit. (4) circular pursuit. When the moving object rotates circularly, so does the camera. ⑤ Oblique pursuit. When a moving object falls from a height, the camera can follow obliquely. ⑤ Zoom tracking. When the photographer faces the oncoming moving object, he uses a zoom lens to follow the shooting in a zoom way. At this time, there will be radiation around the moving body, which has an explosive effect and is very dynamic. The key point of shooting is: when the moving object is clearly focused, the lens is pulled from far to near, that is, from short focal length to long focal length. If the moving body moves backward, the lens can also be pulled from near to far, that is, from long focal length to short focal length. When zooming, the left hand pulls the focal length, the right hand presses the shutter, and the shutter is pressed while pulling the focal length. The background should be scenic, so that lines with generating style can appear when zooming. Pay special attention to safety when shooting, because the moving object is coming. In order to avoid the collision of passive objects, it is necessary to use telescopic zoom lens when shooting long-distance and fast-moving objects. The camera can be fixed on a tripod and zoom at a slow speed during long exposure.