What is the role and function of photographic focal length?

First, the focal length function and function of wide-angle and ultra-wide-angle photography

1, the depth of field is large, which is beneficial to express the subject with deep depth.

2. Wide viewing angle is conducive to shooting a wide range of scenery at close range, especially in urban shooting.

3. The deep scenery has a strong proportion of near-big and far-small contraction, and the picture has a strong sense of perspective.

4. Image distortion varies greatly, especially at the edge of the picture.

Second, the function and role of telephoto and ultra-telephoto

1, the depth of field is small, which is beneficial to absorb the influence of the combination of virtual and real.

2. The viewing angle is small, which can capture the great influence of the scene from a distance and is not easy to interfere with the subject.

3. It can reduce the depth ratio of the near-big-far-small scene, make the front and back still life on the picture compact, and compress the depth sense of the picture perspective.

4. The difference of image distortion is very small.

Extended data

When the camera lens is adjusted to infinity, it is actually a nominal focal length. In design, the distance between the main plane of the lens and the negative or imaging sensor is adjusted to the length of the focal length, and then the image far away from the lens can form a clear image on the negative or sensor. When the lens wants to shoot a close object, the actual focal length of the lens changes.

The focal length is usually marked in millimeters (mm), but you can still see that some old lenses are marked in centimeters (cm) or inches. The size of the field of view depends on the ratio of lens focal length to film size. Because the most popular specification now is 35mm, the field of view of the lens is often marked according to this specification.

The fields of view of standard lens (50mm), wide-angle lens (24mm) and telescope head (500mm) are different. The same is true for digital cameras, whose photoreceptors are smaller than the traditional 35mm film, so they can get the same image with a shorter focal length.

Baidu encyclopedia-focal length