Introduction course of digital SLR camera photography exposure

The English name of Exposure is exposure, and the exposure mode is the mode that the computer uses natural light source, which is usually divided into various modes, including shutter priority, aperture priority, manual exposure, AE lock and so on. The quality of the photo is related to the exposure, that is, how much light is needed to make the CCD get a clear image. Exposure and illumination time (determined by shutter speed). The following is an introductory tutorial on photographic exposure of digital SLR cameras that I have compiled for you. Welcome to refer to ~

The English name of the introduction course of digital SLR camera photography Exposure is exposure. Exposure mode is the mode in which computers use natural light sources, which is usually divided into various modes, including shutter priority, aperture priority, manual exposure, AE lock and so on. The quality of the photo is related to the exposure, that is, how much light is needed to make the CCD get a clear image. Exposure is related to light passing time (determined by shutter speed) and light passing area (determined by aperture size).

In order to get colorful and bright images, it is necessary to properly expose the photoreceptors (films in the traditional era, CCD or CMOS originals in the DSLR era). The so-called exposure is to expose the photoreceptor to a certain amount of light in a certain period of time.

The risk is calculated as follows:

Exposure = light quantity (light intensity allowed by aperture) x time (time length allowed by shutter)

In other words, a complete exposure program consists of the size of the aperture and the timing of the shutter.

At present, the so-called standard exposure value of exposure meter design is to average the exposure of the whole picture to the middle gray level, that is, 18% gray level. The brightness of the middle gray (the intensity of reflected light) is close to the skin color of people or the blue of the sky. By observing the "grey card", we can know the general performance of medium grey.

Generally speaking, to get a correct exposure now, we usually use the built-in exposure meter of the camera to help us calculate the appropriate aperture and shutter combination. The exposure meter averages the measured spotlight light to intermediate gray level through different metering methods, and then adjusts the aperture shutter to achieve the purpose of correct exposure.

From left to right are average metering, central key metering and spot metering.

In order to get the right exposure, you need the right combination of shutter and aperture. When the shutter is fast, the aperture will be larger; The aperture is smaller when the shutter is slow. Shutter priority refers to the exposure value calculated by the automatic metering system of the machine, and then automatically determines how much aperture to use according to the shutter speed you choose. Aperture priority refers to the exposure value calculated by the automatic metering system of the machine, and then automatically decides how many shutters to use according to the aperture size you choose. When shooting, users should balance the exposure and shutter according to the actual environment, which complement each other.

The combination of aperture and shutter forms exposure, which is not unique under certain exposure conditions. For example, the current normal exposure combination is F5.6 and 1/30 seconds. If the aperture is increased by one step, that is F4, the shutter value at this time will become 1/60, and this combination can also achieve normal exposure. Although different combinations can achieve the same exposure, the pictures taken have different effects.

Exposure meters made by DSLR generally have the following metering methods:

Average photometry: average photometry calculates the spotlight of the whole picture, and then gets the intermediate gray value.

Center key photometry: Center key photometry takes the center of the picture as the main weighting part, and then it is supplemented by the surrounding spotlights, and then the intermediate gray value is calculated.

Spot metering: Spot metering only intercepts about 3% ~ 5% of the center of the picture to calculate and find the middle gray value of this point, which is quite convenient for shooting complex ambient light.

Zone metering: Each camera manufacturer will develop its own unique zone metering method to meet the exposure calculation of light in different fields of view, such as Canon's 2 1 zone metering or Nikon's 3D matrix metering. These photometry programs will change and calculate according to different environments to find out the most suitable exposure.

Canon's 2 1 zone metering (source: Canon website, Japan)

In front of us, we have opened the aperture and shutter for everyone. It is mentioned that the difference between the number of each aperture and the number of each segment of the shutter is called one level, one grid or one gear. Whether it is aperture or shutter, the exposure difference at each stage is the same, that is to say:

F4 and F5.6 are at the same level, and115s and 1/30s are at the same level. The amount of light in these two cases is the same.

The difference between F5.6 and F 1 1 is two levels, and the difference between 1/60s and 1/250s is two levels. The difference in light quantity between the two cases is also the same.

In this way, after determining the exposure combination, the number of segments of the aperture and shutter can still be increased or decreased without affecting the final exposure value. Let's take a look at the following examples:

Suppose that the exposure combination we are measuring now is F5.6, 1/250s, but in order to take a portrait with a large aperture and obtain a shallow depth of field, we can change it to F2.8,11000s.

Among them, because the aperture is advanced by two levels (F5.6 >; F4 & gt； F2.8), so the relative shutter should be back two steps (1/250s.

Manual exposure mode

Manual exposure mode requires manual adjustment of aperture and shutter speed every time shooting, which is beneficial for photographers to create different picture effects. If you need a picture of the motion track, you can lengthen the exposure time, speed up the shutter and increase the exposure; If you need to create a dim effect, you should speed up the shutter and reduce the exposure. Although this kind of autonomy is high, it is inconvenient and does not allow time to capture fleeting scenes.

AE mode

AE is called automatic exposure, which means automatic exposure. Modes can be roughly divided into aperture priority AE, shutter speed priority AE, program AE, flash AE and depth priority AE. Aperture priority AE mode is an automatic exposure mode in which the photographer manually selects the aperture size when shooting, and the camera automatically selects the appropriate shutter time according to the scene brightness, CCD sensitivity and manually selected aperture, that is, the exposure mode in which the aperture is manual and the shutter time is automatic. This exposure method is mainly used for shooting occasions that need to give priority to depth of field, such as shooting landscapes, portraits or macro photography.