What is a wide-angle lens?

A wide-angle lens is a short-focus lens. Wide-angle lens and zoom lens are two concepts. Large zoom lens has the characteristics of wide angle and narrow angle. Wide-angle lens generally specifies the focus lens. Photographic lenses with different focal lengths have different performance and modeling characteristics. Photographic lenses with different focal lengths have different viewing angles, image magnification, depth of field and spatial perspective. The modeling characteristics of standard photographic lens are close to the visual effect of human eyes. The characteristics of wide-angle lens and narrow-angle lens are introduced as follows:

First, focal length and viewing angle.

Short-focus camera lens has wide viewing angle and small imaging, while telephoto camera lens has narrow viewing angle and large imaging. The range of scenery that the eyes can reach is the field of vision or field of vision. An imaginary cone formed between the visual field and the viewpoint is the visual angle. In real life, the human eye has a certain field of vision to observe the scenery. Only when the object is on the edge of our field of vision can we see clearly. Objects are imaged on the film through a photographic lens to form a picture. All visible parts of the picture constitute the field of view of the camera lens, and the field of view coincides with the scene angle of the lens.

Second, the focal length and image magnification (image size)

The focal length of a photographic lens is inversely proportional to the viewing angle and field of view, and directly proportional to the image magnification, that is, the longer the focal length, the narrower the viewing angle and the smaller the field of view, and the narrower the spatial range of the scene shot by the photographic lens, and the larger the image formed by the scene. On the contrary, the shorter the focal length, the wider the viewing angle, the larger the visual field, the larger and wider the spatial range of the scene, and the smaller the magnification of the image formed by the scene. That is, shooting the same scene at the same shooting point (the shooting distance is the same), and shooting the scene with a long focal length camera lens has a small range, but the image magnification is large (that is, the viewing angle is large). When shooting with a short focal length camera lens, the scene range is large, but the image magnification is small. Therefore, short focal length camera lens is also called wide-angle camera lens. In order to obtain the expected shooting range (scene) and image magnification, the photographer can choose the appropriate focal length of the camera lens on the premise that the shooting point remains unchanged.

Third, the focal length and shooting distance

When shooting, photographers need different shooting distances (the distance between the camera and the subject) if they want to get the same image magnification and different focal lengths of the camera lens. When the image magnification of the scene is the same, the focal length of the photographic lens is proportional to the object distance. That is, the shorter the focal length, the closer the shooting distance. On the contrary, when shooting with a long focal length camera lens, if the same image magnification is obtained, the farther the shooting distance is required. Therefore, the long focal length camera lens is also called telephoto. If the 135 camera takes a banner photo of a person with a height of 1.60m, and the whole body just fills the height of the shot, then use the 55438+035 camera. When shooting with a lens with a focal length of 100mm, the shooting distance is required to be 6.8 meters, and when shooting with a 200mm lens, the object distance is 13.6 meters. If the distance exceeds this, the person will not be able to fill the height of the shot picture. If the distance is shorter than this, a part of the person's body will be out of the picture.

When shooting, if the shooting distance is limited, the photographer can't choose freely, but if you want to get the expected image magnification, you can choose different focal lengths to achieve it. If the shooting space is narrow and the subject is close to the photographer, it is advisable to use a wide-angle camera lens to shoot, which can not only capture the expected image magnification, but also obtain a larger spatial range of the scene. On the contrary, if the subject is far away from the photographer (that is, the shooting distance is large) and cannot reach the front, a camera lens with a long focal length can be used to shoot, so that a larger image can be obtained on the screen without making the screen space too wide. For example, children in the distance are playing games, and they don't want to disturb them, so that they can be in a normal game state and want to get a bigger image. Only a camera lens with a long focal length can complete it.

Fourth, focal length and viewing angle.

The scenery seen by human eyes is composed of objects with different spatial positions and a certain distance from each other. And each object has its own three-dimensional shape and contour shape. Our photographic picture represents three-dimensional space in a two-dimensional plane, not only the spatial distance relationship between objects, but also the three-dimensional shape of the objects themselves. How to make people's eyes correctly judge the spatial relationship and three-dimensional form between the original scenes through the observation of photographic images is our photographer's primary task, which can break through the visual experience of human eyes and achieve special artistic effects.

When we stand on a straight road and look into the distance, we will feel that the cars on the road are getting bigger and bigger as they get closer to us and smaller as they get farther away from us. The width of the road becomes narrower and narrower with the distance of the road. As the road extends far away, the two sides of the road gradually approach each other, concentrate and finally converge on the horizon. In addition, it is not difficult to find that the closer the street lamp is to us, the fewer, thinner and denser the lights are, and the farther the lamp post is from us, the shorter it will be, and finally it will converge, converge and converge towards the horizon until it disappears. In short, in life, we observe objects of the same size from a certain position, because they are different from our position, so their sizes are different. This visual phenomenon is called line perspective. When our eyes watch the images formed on the photographic screen, we imagine in our minds through the perspective relationship and occlusion relationship between various object images, so as to judge the real space where the photographed scene is located and the real size of the object, resulting in the three-dimensional sense of space and the three-dimensional sense of the object on the two-dimensional plane. When the image magnification of the same object in the picture is very different, the stronger the perspective relationship of the image, we think that the greater the distance between them and the farther away from each other, the stronger the sense of spatial depth of the picture, and vice versa.

In addition to line perspective, there is also air perspective, which are all factors that affect the sense of spatial depth of the picture. I won't go into details in this article, but there are many factors that determine line perspective. This paper only discusses the relationship between focal length and line perspective from the relationship between shooting distance, lens focal length and screen scene.

1, object distance and line perspective

According to the image magnification, the image magnification of the objects in different spatial positions in the shooting scene is different because of the different object distances. The closer the object distance is, the greater the image magnification is, and the farther the object distance is, the smaller the image magnification is. Obviously, when shooting a scene on the same film, objects in different spatial positions have a perspective relationship of "near big and far small" due to different image magnifications, and there is also a certain perspective relationship between different parts of each object. For example, when shooting a high-rise building on the facade, because the distance between the high and low parts of the building is different from the lens, the corresponding perspective effect is produced, which makes it have a modeling effect close to the normal visual effect of human eyes. Therefore, the object distance is the main factor that determines the perspective relationship of images.

2. When the magnification of the object image is constant, the relationship between focal length and perspective.

As we all know, under the condition that the image magnification of the subject in the picture is unchanged, shooting with lenses with different focal lengths requires different object distances. The longer the focal length of the camera lens, the more the object distance should be increased, and the ratio of the object distance of the back scene to the object distance of the foreground will be reduced, and the image magnification of the close scene will be obviously reduced, while the image magnification of the distant scene will be obviously increased, so that the difference between the image magnification of the front and rear scenes will be reduced and the magnification of the subject will be close. On the contrary, the shorter the focal length of the camera lens is, the smaller the object distance is, and the ratio of the object distance in the background to the object distance in the foreground is obviously increased, which makes the difference of image magnification between the front and rear scenes increase. Whether the perspective effect of the shot picture is strong or not depends on the difference of image magnification of the scene before and after. Therefore, when the image magnification of the subject in the picture remains unchanged, the perspective effect of the picture shot by the short-focus camera lens is obvious and the sense of spatial depth is strong, while the perspective effect of the picture shot by the telephoto camera lens is weakened and the sense of spatial depth is weak, which seems to crowd the scenes together.

3. The relationship between focal length and perspective under the same shooting distance.

At the same shooting point, lenses with different focal lengths have the same object distance and the same perspective relationship to the picture taken in the same scene, and the picture taken by the long focal length photographic lens only magnifies a part (or object) of the picture taken by the short focal length photographic lens. However, due to the wide viewing angle of the short-focus camera lens, it can bring a wider scene around the subject into the picture, and more importantly, it can bring more enlarged foreground into the picture, so that the audience can associate more scenes from the picture. Therefore, the wide spatial range and rich scene levels make people feel that the space of the picture is very broad and far-reaching, which has a strong spatial visual effect and gives people the illusion that the perspective effect of the picture seems to be enhanced. Therefore, in order to obtain a strong perspective effect, we must choose a multi-layer scene with different object distances. The closer the object distance is, the more obvious the perspective effect is.

Verb (abbreviation for verb) focus and depth of field

When we focus on a certain point of the subject, the image of that point is the clearest, and the images of all points in space before and after focusing should be similar. Therefore, the images of other objects in a certain range before and after the focus distance are not the most realistic, but they are not the most blurred. Then, this clear range before and after the focus target is called depth of field. The existence of depth of field makes the lens have the ability to truly reproduce the visual experience. Blurring the picture, in fact, our visual resolution is not high. Within a certain distance, our vision regards it as a clear shadow of the contrast between reality and reality, which is an indispensable means to highlight the subject and create a sense of space.

The factors that affect the depth of field are usually lens focal length, object distance and aperture. When the object distance and aperture are constant, the longer the focal length of the lens, the smaller the depth of field; The shorter the focal length, the greater the depth of field. When the lens focal length and object distance are the same, the larger the aperture value, the greater the depth of field; When the focal length and aperture of the lens are constant, the greater the object distance, the greater the depth of field.

References:

Expression method of camera modeling