What is depth of field?

Depth of field:

When the lens focuses on a certain point of the object being photographed, the object at this point can be clearly imaged on the TV screen. Scenery within a certain range before and after this point can also be recorded more clearly. Beyond this range it becomes unclear. This means that there is a certain limit to the clear range of the scene captured by the lens. The depth range of the photographed object recorded "more clearly" by the lens is the depth of field. When the lens is pointed at the subject, the clear range in front of the subject is called foreground depth, and the clear range behind it is called back depth of field. The foreground depth and the back depth of field combined, that is, the depth of the entire TV picture from the nearest clear point to the farthest clear point, is called panoramic depth.

In some pictures, the front of the subject is clear but the back is blurry; in some pictures, the back of the subject is clear but the front is blurry; in other pictures, only the subject is clear but the front and back are blurry. , these phenomena are 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 photography. Correctly understanding and using depth of field will help you take satisfying pictures. There are three main factors that determine the depth of field:

1. Aperture

When the focal length of the lens is the same and the shooting distance is the same, the smaller the aperture, the wider the range of the depth of field; the larger the aperture. , the smaller the range of depth of field. This is because the smaller the aperture, the thinner the light beam entering the lens, the more obvious the paraxial effect, and the smaller the angle at which the light converges. This is done before and after imaging. The concentrated light will leave a smaller spot on the imaging surface, making the original unclear scenes closer and farther from the lens have 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 range; the longer the focal length of the lens, the smaller the depth of field range. This is because a lens with a short focal length has a much narrower focus zone (depth of focus) for light coming from objects at different distances in front and back than a lens with a long focal length, so more light spots will enter acceptable sharpness. area.

3. Object distance

When the focal length and aperture coefficient of the lens are equal, the farther the object distance is, the greater the depth of field range; the closer the object distance is, the smaller the depth of field range is. This is because the scenery far away from the lens requires only a few adjustments to achieve clear focus, and the front and rear scenery are tightly focused. This will bring more light spots into the acceptable sharpness 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 is enlarged, that is, the depth of focus range is expanded, thus reducing the light spots entering the acceptable sharpness area and reducing the depth of field. For this reason, the foreground depth of a lens is always less than the back depth of field.