What is the key point in photography?

Focus, in physics, refers to the convergence point of parallel light after refraction by lens or reflection by curved mirror.

In photography, in fact, the use of focus in the shooting process is the same as the focusing principle in physics, which reflects the difference of subject and focus, as well as the different shooting themes of scenes, people and things.

There are two ways to determine the position of two focal points. One is the front focal length and the back focal length relative to the first and last surfaces of the system. The front focal length is the distance from the object focus to the first surface of the system, and the back focal length is the distance from the image focus to the last surface of the system.

Another method is relative to the main plane of the system, that is, the so-called main focal length, object main focal length or first main focal length, which is the distance of object focal length relative to the first main plane of the system, and image main focal length or second main focal length is the distance of image focal length relative to the second main plane of the system.

The focal length value of a system often refers to the main focal length value. The plane perpendicular to the common axis of the optical system and passing through the focal point is the focal plane. Because there are two focal points, there are also two focal planes: the first focal plane (object focal plane) and the second focal plane (image focal plane).

Extended data

1. Plant shooting: focusing on flowers.

Flowers are undoubtedly the most attractive and beautiful part of growing pearls. So it is not difficult to understand that flowers are the most common focus choice in plant photography.

But when facing a bunch of flowers, we should first consider the most distinctive ones, such as the most beautiful ones, or the colors are different from other flowers; Then you can choose a flower that is slightly higher or closer to the camera than other flowers by observation. Through these methods, we can highlight this flower and make it an interesting center of the picture.

2. Take flowers at close range: Focus on stamens.

Close-up shot of flowers, the focus should clearly fall on the flower core. At this time, the close-up of the flower is enlarged, and the original colorful petals in the photo are mostly used as foil, while the delicate stamens in the flower core are arranged in an extremely regular way, which becomes a fascinating place.

3. When shooting close-ups, eyes are the key point.

Close-up photos of people are generally half-length photos focusing on people's faces. This kind of photos need to depict the character and even the heart through expressions.

When shooting close-ups of people, eyes are the first choice of focus. When a person's face is facing the camera, both eyes are on the same plane at this time, and either eye can focus; But this kind of framing will be peaceful, and then it will appear ordinary, so most photographers will take a half-side view of people and shoot it.

At this time, people's eyes will be in tandem. At this time, you need to focus on the eyes close to the camera for focusing shooting. Because its position is obviously more important than the eyes at the back.

4. When taking a full-length portrait of a person, the head is an important focus.

When shooting portraits including the whole body and the environment, the human eye can't focus clearly, so the key to choosing the focus quickly and conveniently is to focus on the head of the person.

Whether it is to show the movements or postures of the characters, the five senses of the characters are the key in the picture. Every move of people is controlled by the brain, so the head will become the center that affects the whole body. When shooting, you can focus on the face or head of the person in advance, and then quickly re-compose the picture when the whole body posture of the person reaches the ideal state.

5. Take photos of people and the environment: it is best to focus on people.

Such photos include simple souvenir photos, documentary photos and commercial photos. The photos of the combination of man and environment are the most vivid and the most difficult to take. However, whether people are the main body or the foil, most of these photos are taken with people as the focus, because people are the most active and emotional compared with those landscapes that are not moving or moving slowly.

Of course, when shooting with people as the focus, we should also pay attention to the depth of field to control the change of the actual environment. If people and scenery are simply needed to be clear, we can use a small aperture to obtain a large depth of field.

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