What is the function of depth of field lens?

The depth of field lens makes it much more convenient for us to take pictures in our lives. Its function is to accurately focus the range within a certain range. Blur the secondary factors in the background and highlight the main body when taking pictures. Moreover, the aperture is getting bigger and bigger, and the depth of field is getting shorter and shorter, which is a common photography method. At present, this kind of lens will be available on relatively high-end mobile phones.

In optics, especially in video recording or photography, the depth of field (DOF) is a range of distances that can be clearly imaged in space. Depth of field is the range of good focus. It can highlight the subject by blurring the background, and can also shoot a clear background.

The depth of field lens makes it much more convenient for us to take pictures in our lives. Its function is to accurately focus the range within a certain range. Blur the secondary factors in the background and highlight the main body when taking pictures. Moreover, the aperture is getting bigger and bigger, and the depth of field is getting shorter and shorter, which is a relatively common lighting method. At present, this kind of lens will be available on relatively high-end mobile phones.

The distance between the nearest clear image and the farthest clear image of the camera lens is the focus. The range of clear imaging at this distance is called depth of field lens. Depth of field depends on three elements, aperture, focal length and object distance. Ultra-wide-angle lenses have great depth of field at almost all apertures, while telephoto lenses have very limited depth of field even at the smallest aperture.

First, large depth of field

Large depth of field means that a lens can keep other scenes clear before and after the scene. Among them, the camera lens adopts a small aperture, a short focal length and a long distance between the subject and the lens, which are necessary conditions for creating a large depth of field. One of the most important functions of large depth-of-field lens is to establish the implied relationship between foreground and background; Secondly, a large depth of field can also expand the screen space, present a sense of depth, create a visual impact, enrich the screen content and convey more information to the audience. In the famous "Citizen Case" scene, there is no doubt that the main body of the picture is a mother and a lawyer, who are discussing the future of Kane Jr. Mother occupies an absolute dominant position and is in the focus of composition. Little Kathy's father behind the main body seems a little anxious and helpless. Because he has no right to decide whether Kane will stay or not, he plays the role of a companion. In the deepest part of the picture, little Kane is playing with snow outside. By comparing the relationship between foreground and background, we can find that the freedom of little Cathy outside the window is only the last swan song. His childhood is coming to an end, and he is strangled by the contract between his mother and his lawyer, which is located in the western prospect and plays a role in pointing out the theme: Kane's life is about to change dramatically. In other words, excellent directors who are good at expressing artistic purport through careful setting of depth of field, such as Memories of Murder, often use large depth of field to set information in the West. In the early stage, the thunder calendar of rural police officers was popular as the foreground, and urban police officers only accounted for a small part of the west as the background, which reflected the unequal status of the two; In the later stage, the proportion of the two tends to be balanced to show the changes in their emotions and handling methods. It can be said that the information that the director wants to convey has already been contained in the picture elements, waiting for the audience to explore, and this is precisely the uncertainty and ambiguity brought by the depth of field.

Second, the depth of field is small.

When shooting, the small range that keeps other scenes clear before and after the scene is called small depth of field. Depth of field can be affected by adjusting aperture, focal length and object distance. Compared with large depth of field, small depth of field has the characteristics of large aperture, short focal length and the subject is closer to the lens. In practical application, it can blur the foreground and background images of the subject, highlight the subject, blur the background and environment, and create a soft impression. Therefore, in many film and television dramas, small depth of field is often used to highlight the guest appearance of stars, thus beautifying the characters and shaping the effect. In the use of film language, small depth of field can make the local distant scene clear in the deep space, and enrich the expressive force and appeal of the focal plane to a greater extent. Some film directors use small depth of field to narrow the distance between people when dealing with multi-person scenes, showing the closeness and compactness between the subjects. This is because the layering of small depth of field is weakened: the distance between foreground and background seems to be filled. Therefore, the characters and scenery in the picture often have a crowded, compact and cordial feeling. For example, a close-up of Yang Guifei looking back in The Legend of the Demon Cat left a deep impression on the audience. The background is all blurred, the audience's attention is completely attracted by the subject, and the characters become the ideographic center of the picture, highlighting the beauty of Yang Guifei.