What function should a picture use to blur the background in SLR photography? For example, a person standing in front of the sea, I want to make people clear, let the sea and the beach.

This function is called depth of field control.

The less depth of field you need.

Three elements of depth of field control: aperture, focal length and distance. They are described as follows:

1. Aperture, the larger the aperture, the smaller the depth of field. You need to open the aperture as wide as possible. If the lens is low-grade, the maximum aperture is usually very small, such as F4 or F5.6, and it is difficult to get the desired effect.

2. Focal length, the greater the focal length, the smaller the depth of field. You need to use the telephoto end of the lens as much as possible (the bigger side of the person). If you use a wide-angle card machine, the maximum focal length is usually relatively small, which can't meet your wishes.

3. Distance, the greater the relative distance between the subject and the background (foreground), the smaller the depth of field. This is a relative value. In short, keep the subject away from the background or foreground.

Usually this kind of picture needs a fixed focus lens to shoot.

The second question:

By default, the focus is in the middle of the screen.

When the subject is not in the middle, there are two basic methods:

1. First put the subject in the middle, half press the shutter, turn the camera to make the required composition, and then press the shutter completely to shoot (this is called focus lock);

2. Make a composition first, then move the focus to the main body that is not in the middle, and press the shutter half-way until the focus is completed.

In addition, some machines have the function of face recognition, so people can focus on it everywhere.