What is the focal length? What role does it play in photography?

The focal length refers to the interval between the center of the lens and the focal point, that is, the position of the camera film (focal plane). The longer this interval, the greater the imaging, and the farther the interval, the smaller the imaging. The so-called 28mm, 50mm, 70mm, 200mm lenses, etc. refer to the right and wrong of the focal length.

According to the size of the diagonal of the film used, it is divided into standard lenses, long focal length lenses, short focal length lenses, etc. For example, the film of the 135 camera we use is about 50mm diagonal, so its standard lens is about 50mm, and the ** shot is consistent with the scene you actually see, including the proportion of the size of the object, the range you see, etc.; When the focal length of the lens is larger than this standard, such as 200mm focal length, the angle of view of the shot is smaller than the angle of view of your eyes, the shooting range will be reduced, and the subject will be larger, which is a long focal length lens. When the focal length is less than 50mm, such as 28mm, the angle of view of the shot is larger than the angle of view of your eyes, and the shooting range is also large, and the subject of the shot is not prominent in the frame, it will appear smaller than it actually is, which is a short focal length lens.

As for what lens to use when shooting, it depends on what you are shooting for? Use a short focal length lens for large scenes; When highlighting the subject, use a telephoto lens; For realistic scenes, standard lenses are used. The blurred background of telephoto shooting means that the depth of field range is small, that is, the emotional range.

When shooting, we will get that the front and back of the subject are clear within a certain range, and this clear range is blurred outside of this clear range, and this clear range is the depth of field. The longer the focal length of the lens, the shorter the depth of field, and the shorter the focal length of the lens, the longer the depth of field.

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In photography, what is focal length?

Focal length refers to the distance from the center of the lens to the focal point where light is concentrated.

Focal length, also known as focal length, is a measure of the concentration or divergence of light in an optical system. It is also the distance from the optical center of the lens to the imaging plane such as the tintle or CCD or CMOS in a camera. Optical systems with short focal lengths have a better ability to concentrate light than those with long focal lengths.

In a thin lens in air, the focal length is the distance from the center of the lens to the main focal point. For a converging lens (e.g., a convex lens), the focal length is positive, and a beam of parallel light will be concentrated at a single point. For a divergent lens (e.g. a concave lens), the rotten focalence is negative, and a beam of parallel light will spread out after passing through the lens.

The application of focal length in photography

When the photographic lens is adjusted to infinity, it is actually a focal length in name only. In terms of design, the distance between the main plane of the lens and the film or imaging sensor is adjusted to the length of the focal length, and then objects at a distance can form a clear image on the film or sensor. When the lens is to photograph a relatively close object, it is the distance between the main plane of the lens and the imaging detector or film that changes, so that the object at a limited distance can be clearly imaged.

Focal lengths are usually indicated in millimeters (mm), but it is still possible to see some older lenses that are marked in centimeters (cm) or inches. The size of the field of view depends on the ratio of the focal length of the lens to the size of the negative. Since the most popular is the 35mm format, the field of view of the lens is often marked according to this specification.

The field of view is different for standard lenses (50mm), wide-angle lenses (24mm), and telephoto lenses (500mm). The same is true for digital cameras, where the sensor is smaller than conventional 35mm films, so the same image can be obtained with a shorter focal length.

Focus: The point at which parallel rays of light converge on the optical axis after being refracted through the lens. Focal length f: The distance between the focal point and the center of the lens.

Focus: The point at which parallel rays of light converge on the optical axis after being refracted through the lens. Focal length f:

The distance between the focal point and the center of the lens. Image distance u: the distance between the imaging plane and the center of the lens, its general rule is:

f, the distance between the photographic object and the lens is called the object distance, and the distance between the imaging plate and the lens is called the image distance rather than the focal length.

The concept of focal length

Focal length, also known as focal length, is a measure of the concentration or divergence of light in an optical system, and refers to the distance from the center of the lens to the focal point of light concentration when collimated light is incidence. In a camera, the focal length is the distance from the optical center of the lens to the imaging plane such as the radicle, CCD, or CMOS. The focal length of a camera lens is divided into image-side focal length and object-square focal length.

The focal length of the image square is the distance from the main surface of the image square to the focal point of the image square, and similarly, the focal length of the object side is the distance from the main surface of the object to the focus of the object side. The focal length of a lens determines the size of the image of the subject captured by the lens on the imaging plane.

Assuming that the same subject is shot at the same distance, the longer the focal length of the lens, the greater the magnification of the image on the film or sensor.

1. Functions and functions of focal lengths for wide-angle and ultra-wide-angle photography.

1. The large depth of field is conducive to the performance of the subject with a large depth.

2. The large angle of view is conducive to taking in a wide range of scenery at close range, especially in urban shooting.

3. The ratio of near and far shrinkage of the deep scenery is strong, and the sense of perspective is strong.

4. The image distortion is quite different, especially at the edge of the picture.

2. The focal length function and function of telephoto and Teno ultra-telephoto photography.

1. The depth of field is small, which is conducive to absorbing the influence of the combination of virtual and real.

2. The angle of view is small, which can capture the greater impact of the framing of the brother from a distance and is not easy to interfere with the subject.

3. It can reduce the proportion of the near and far of the deep scene, so that the front and rear still life are compact on the picture, and the sense of depth of the picture perspective is compressed.

4. The image distortion is small.