How to choose the focal length of the lens in portrait photography

1. Perspective deformation and sense of space: the focal length is too short, and it is easy to have perspective deformation; On the contrary, if the focal length is too long, the compression will be too great. 85mm is just right.

2. Operating distance and mobility: Because the fixed focal length lens cannot be like a zoom lens, the size of the subject can be changed without changing the position of the photographer. For example, if you want to shoot from the whole body to the big head, the longer the focal length, the longer the distance you need to move, and the maneuverability will be reduced.

85mm is just short enough to operate at a distance, so the maneuverability is high enough.

Note: Some readers may ask why human zoom is so annoying, because each focal length has its own sense of space, which cannot be replaced by other focal lengths.

3. Large aperture: Because of physical limitations, it is difficult for long focal length lenses to achieve a large aperture beyond f, while the 85mm maximum aperture can be held to f.

Focal length refers to the distance from the center point of the lens to the imaging plane, such as the film or image sensor that forms a clear image.

The focal length is expressed in the unit "mm". For example, the 50mm lens is the distance between the center point of the lens of the large lens and the imaging plane such as the film or image sensor that forms a clear image, that is, the focal length is 50mm, which is not adjustable, and it is also called a fixed focal length lens, while the 18-50mm lens refers to the adjustable focal length of this lens between 18-50mm, also called a zoom lens.

1.A lens with a focal length of 40-60mm is called a standard lens, and the ** shot at this focal length is basically the same as what the human eye sees, around 45°.

2.Lenses with a focal length of less than 40mm are called wide-angle lenses, and the visual angle shot by this focal length segment is greater than the angle of the human eye, greater than 60°.

3.Lenses with a focal length greater than 60mm are called telephoto long-beam lenses, and the ** visual angle shot in this focal length segment is smaller than the angle of the human eye, less than 30°.

4.A fisheye lens is a lens with a very short focal length and an angle of view close to or equal to 180°, and a lens with a focal length of 16mm or less is generally considered a fisheye lens.

5.A macro lens is a lens with a reproduction ratio of approximately 1:1, and it can be a lens of any focal length, and it can focus on a closer subject than a general lens, creating a life-size image on the imaging plane.

1.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 (the smaller the angle of view) of the image created by the subject on the film or image sensor.

2.The longer the focal length, the less light reaches the sensor, and the darker the image.

3.We know that for a camera, the larger the aperture, the greater the amount of light and the brighter the picture. However, for focal lengths, the longer the focal length, the less light reaches the sensor.

Therefore, the brightness of a picture with orthostatic is related to the aperture and focal length, so how to consider it in reality? This is where the f-number comes in, which is the relative value of the focal length of the lens and the diameter of the lens's transmission. Regardless of the lens, as long as the f-number is the same, the amount of light reaching the image sensor is the same.

4.The longer the focal length, the smaller the depth of field. As you can see from the figure below, when the subject is 10 meters away from the camera, the depth of field (red) is the longest at a focal length of 28 mm, followed by the depth of field at a focal length of 70 mm, and the shortest depth of field at a focal length of 200 mm.

What do you mainly shoot?

Generally speaking, since the angle of view of a standard lens is the same as that of the human eye, the first lens of a camera should be the header.

For a 135 camera, the focal length of the header is 50mm.

For example, if you shoot the same subject, you need to have the same size in the composition, which means that the lens with different focal lengths will have different backgrounds of the lenses.

Fisheye lenses with shorter focal lengths can even capture the photographer's feet into the frame.

Telephoto lenses with long focal lengths have a smaller angle of view, and like a telescope, they can compress the background distance between the subject and its backdrop, making it feel close.

In general, a wide-angle lens with a short focal length is used for shooting scenes, and a telephoto lens with a long focal length is used for portraits.

1. Under normal circumstances, in the monitoring environment of ordinary conference rooms, offices and elevator rooms, short-range fixed focal length lenses of about 3mm to 12mm can meet the needs.

2. For security monitoring in the community, or ordinary road monitoring, 6mm to 15mm monitoring lenses can basically meet the needs.

3. For general intersection monitoring, due to the large shooting space and high definition requirements, it is suitable for medium-distance focal length lenses from 6mm to 60mm.

4. On the camera lens used for urban security monitoring, due to the difference in monitoring distance and environment, it is basically equipped with a long-distance zoom lens of about 10mm to 120mm.

5. It is used in highway, national highway, river, airport, forest and other fields with large-area monitoring needs, in the above environment, the monitoring range is far from the main feature of these environments, so the lens of 10mm to 1100mm is generally selected to meet the shooting needs.

In addition, in the imaging characteristics of the lens, the larger the focal length, the farther the monitoring, but the smaller the viewing angle; The smaller the focal length, the closer the monitoring distance, and the larger the field of view, so this is a contradictory relationship, and the distance and angle can only be taken one.

Therefore, when choosing a focal length, it is often measured according to the angle of view of the shot. A starting focal length that is too large or too small may have a detrimental effect on the effectiveness of monitoring.

In different use occasions, the lens of the camera is selected according to different use requirements.

Conventional camera lenses are as follows:

1) Manual aperture prime lens. The aperture of this lens can be changed, but the focal length cannot be changed. It is suitable for occasions with a fixed focal length and little change in light illumination.

2) Manual aperture zoom lens. The application method is the same as above, except that in some cases, the lens used is not determined, taking into account the range and distance of the camera environment.

3) Auto-aperture prime lens. When the ambient illumination changes, this lens drives the lens aperture motor through the signal amplitude output by the camera's brightness level to automatically adjust the size of the aperture to ensure that the illumination falling on the CCD target surface is constant. It is suitable for occasions with large changes in illumination and fixed camera focal length.

4) Auto-iris zoom lens. The application method is the same as above, except that in some cases, the lens used is not determined, taking into account the range and distance of the camera environment.

5) Motorized zoom, motorized aperture, motorized focal length lens - three variable lenses. The adjustment of the aperture and focal length of this lens is controlled by electric power, the lens generally has a longer focal length, a larger zoom range, the aperture can be controlled, and it can be controlled by remote control, so the lens has a large range of application, but because it is expensive, therefore, the number of uses in general engineering is limited.