How to enlarge the depth of field in photography? Thank you.

When the lens focuses on a certain point of the object, the object at that point can be clearly imaged on the TV screen. Scenery in a certain range before and after this point can also be recorded more clearly. Beyond this range, it is not clear. In other words, the clear range of the scene shot by the lens is limited. The depth range of the object clearly recorded by the lens is the depth of field. When the lens is aimed at the subject, the clearance range in front of the subject is called foreground depth of field, and the clearance range in the back is called back depth of field. The foreground depth of field and the background depth of field together, that is, the depth of the whole TV picture from the nearest clear point to the farthest clear point, is called Quan Jingshen.

In some pictures, the front of the subject is clear and the back is blurred, in some pictures, the back of the subject is clear and the front is blurred, and in some pictures, only the subject is clear and blurred. These phenomena are all caused by the depth of field characteristics of the lens. It can be said that the principle of depth of field plays an extremely important role in camera shooting. Correct understanding and application of depth of field is helpful to take satisfactory photos. There are three main factors that determine the depth of field:

1. The focal length of the lens is the same, and when the shooting distance is the same, the smaller the aperture, the larger the depth of field range; The larger the aperture, the smaller the depth of field. This is because the smaller the aperture, the thinner the beam entering the lens, the more obvious the paraxial effect and the smaller the angle of light convergence. In this way, the converging light in front of the imaging plane will leave a smaller spot on the imaging plane, so that the scenery that was not clear from the lens has acceptable clarity.

2. Focal length When the aperture coefficient and shooting distance are the same, the shorter the focal length of the lens, the greater the depth of field; The longer the lens focuses, the smaller the depth of field range. This is because the focal zone (focal depth) formed by the lens with short focal length is much narrower than that of the lens with long focal length, so more light spots will enter the acceptable definition area.

3. When the focal length and aperture coefficient of the object distance lens are equal, the farther the object distance is, the wider the depth of field is; The closer the object distance, the smaller the depth of field range. This is because the scenery far from the lens can be clearly focused with a little adjustment, and the focus of the front and rear scenes is closely gathered. This will allow more light spots to enter the acceptable definition area, so the depth of field will increase. On the contrary, when focusing on a scene close to the lens, the distance between the front and rear focal points increases, that is, the focal depth range increases, so that the number of spots entering the acceptable definition area decreases and the depth of field decreases. For this reason, the foreground depth of a lens is always smaller than the depth of field behind it.