What do these photos (camera, mobile phone) mean? Introduce it.

aperture: it is a device used to control the amount of light that passes through the lens and enters the photosensitive surface in the fuselage, usually in the lens. To express the aperture size, we use f value

to calculate the exposure value in practical photography, which is a scale value corresponding to the aperture value to express the lens' light passing ability.

Because the aperture value changes in multiples of 2, it will be difficult to calculate the exposure value in actual photography if the aperture value is directly used to represent the light flux of the lens. Aperture Value is usually abbreviated as AV (aperture value in English). According to the square value relationship between the area and radius of a circle, it is known that in order to achieve the purpose of adjusting the light flux by multiple, the aperture diameter should be increased by a factor of √2 (approximately equal to 1.4).

Aperture is a device used to control the light quantity of light passing through the lens and entering the photosensitive surface in the fuselage, which is usually in the lens. To express the aperture size, we use f value

to calculate the exposure value in practical photography, which is a scale value corresponding to the aperture value to express the lens' light passing ability.

Because the aperture value changes in multiples of 2, it will be difficult to calculate the exposure value in actual photography if the aperture value is directly used to represent the light flux of the lens. Aperture Value is usually AV (abbreviation of "aperture value" in English). According to the square value relationship between the area and radius of a circle, it can be known that in order to adjust the light flux by multiple, the aperture diameter should be increased in a coefficient relationship of √2 (about equal to 1.4).

Exposure time

exposure time

the time for the shutter to open in order to project light onto the photosensitive surface of photographic photosensitive materials. It depends on the sensitivity of photographic photosensitive materials and the illumination on the photosensitive surface.

The exposure time of a camera refers to the time interval from the opening to the closing of the shutter. During this time, an object can leave an image on the negative.

The exposure time depends on the need, and there is no saying that it is good or bad, only the saying that it is necessary. For example, if you photograph the trajectory of the stars, it will take a long exposure time (maybe several hours), so that the long-term trajectory of the stars will be imaged on the negative. If you want to take a clear picture of a speeding car, it takes a short time (usually a few thousandths of a second).

if the exposure time is long, more light will enter, which is suitable for poor light conditions. Short exposure time is suitable for better light.

the exposure time mainly refers to the exposure time of the negative film. The longer the exposure time, the brighter the photo generated on the negative film, and the darker it is. In the case of dark outside light, it is generally required to extend the exposure time (such as night scene).

the faster the shutter speed, the more you can grab the moving object and make it clearly imaged. When the shutter speed is higher than one-sixtieth of a second, it is best to use a tripod, otherwise the image will be difficult to be clear.

ISO

is the sensitivity of the camera. The film used in traditional cameras has different sensitivity, and the sensitivity of film to light is different with different ISO. Correspondingly, DC also uses different ISO values to set the camera's sensitivity to light (Figure 1). DC has the same ISO value as traditional photographic film, and it is an important parameter to control exposure. ISO value is a measure of the sensitivity of DC to light, which is usually expressed as ISO value. The larger the value, the stronger the photosensitivity, and the smaller the value, the weaker the photosensitivity. Commonly used expressions are ISO25, 5, 1, 2, 4, 8, 16, 32 and so on.

when we use digital cameras, we should make reasonable ISO settings. Generally speaking, under the same shooting conditions, the greater the ISO value setting of DC, the worse the picture quality of photos taken by DC, which is mainly reflected in too much noise. Because the photosensitive elements of DC are mostly CCD, each CCD element has its own inherent sensitivity. When the exposure of DC increases, the CCD increases the gain through the amplifier circuit, but the negative effect of this increase is that the picture noise is also amplified accordingly, which makes the picture quality of the photographed picture worse, that is, the particles we often say become coarse. Moreover, the higher the ISO value, the coarser the particles.

generally, when shooting relatively static things such as scenery, people and macro, we can use relatively low ISO, such as ISO1；, as long as the light allows. When shooting night scenes, you should also use low ISO and shoot on a tripod, and the effect will be much better than directly using the highest ISO.

When shooting instant effects, such as sports competitions and on-site snapping, the shutter speed has to be increased to ensure the clarity of photos. At this time, you can use high ISO settings, such as ISO8；; In order to prevent too much loss of photo details, you can take more photos and then make adjustments. When shooting old people or workers, sometimes in order to show their weather-beaten faces or hands, we can set a high ISO to shoot, so that there is a lot of noise and coarse particles in the photos, which can express special effects.

Exposure compensation

is an exposure control method, which is generally about 2-3 ev. If the ambient light source is dark, the exposure value can be increased (such as +1EV and +2EV). Exposure compensation is a shooting method that consciously changes the "appropriate" exposure parameters automatically calculated by the camera to make the photos brighter or darker. Photographers can adjust the brightness of photos according to their own ideas and create unique visual effects. Generally speaking, the camera will change the aperture value or shutter speed to adjust the exposure value.

focal length

is a measure of light convergence or divergence in an optical system, which refers to the distance from the optical center of the lens to the focus of light convergence when parallel light is incident. It is also the distance from the center of the lens to the imaging plane such as the backplane or CCD in the camera. An optical system with a short focal length has a better ability to collect light than an optical system with a long focal length. Simply speaking, the focal length is the distance from the focal point to the vertex of the mirror.