What is exposure and what is the use of exposure in photography?

Every novice photographer will inevitably encounter overexposure or underexposure. Here comes a question: which parameters will destroy the picture and how to make the picture perfect? The answer is simple: every beginner must first think of the concept of exposure-correctly understand the changes of these parameters under the light in the picture, which is the basis of photography.

First, what is exposure?

The term "exposure" can be interpreted as the amount of light that falls on a photosensitive material at a specific time. In other words, this parameter shows how much light shines on the lens during exposure.

It can be said that exposure itself is not a specific parameter, but an integral part of it, which can be adjusted according to the characteristics of specific shooting, which will be more correct. All the light entering the camera is transmitted to the main exposure parameters. By the way, there are only three-they are also called exposure parameters. We should pay attention to them in the article so as to know the correct exposure.

Second, the exposure parameters that affect the exposure

Exposure is affected by parameters that all photographers know (or should know), regardless of professional level. Talking about the basic knowledge of aperture value, shutter speed and ISO sensitivity. Almost all cameras can automatically control these three parameters, but all digital SLR cameras have manual control function: to provide the greatest possibility when shooting.

For a novice photographer, it seems impossible to understand the purpose of shooting settings: there are too many terms, meanings and rules in this respect, and even the laws of physics will come in handy, so as to quickly understand the functionality of these concepts and how they will easily enter your works.

Stomatal size

The aperture adjusts the diameter of the hole through which light enters the camera matrix. These diaphragm blades can be made of iron or plastic, and they can cover and open the holes in the camera lens. In order to make your photo successful, the matrix needs a certain amount of light every time-aperture value can help complete this task.

It is reasonable to assume that the larger the aperture of the lens is, the more light enters the frame-this option is very suitable for photos in low illumination places. The aperture value is represented by the letter f, followed by a decimal-the smaller the value, the larger the aperture opening, and vice versa. This means that f/2.0 is always higher than f/2.8.

Each possible aperture diameter will mainly affect the depth of field-depth of field. When the value of f is small, the depth of field becomes larger, which means that all objects in the frame look equally clear. If the aperture value is large, most images will become very blurred, and the selected subject will become very clear.

You need to use a smaller aperture value and a larger diameter in low light: don't forget to use a tripod at night and when other artificial light sources can't be used.

Exposure time or shutter speed

Exposure is the time when light enters the matrix. Measured in seconds and fractions of seconds. In addition to changing the amount of light entering the matrix through the camera aperture, we must also control the time when light enters the matrix. In order to get the correct exposure, it is very important to choose the correct shutter speed, aperture value and sensitivity.

The fast shutter speed allows you to open the camera shutter in a fraction of a second, which means that even in motion, this exposure will help to stop or freeze the objects in the picture. If the exposure time is equal to 1 s, the traces and some blurs left on the object will immediately become obvious in the photo-this technology will also appear in works of art. Generally, the shutter speed of SLR cameras has a discrete value: in the range of 15 seconds to 1/2000 seconds, These values will be as follows:15s-8s-4s-2s-1s-160s-1/320s-1500s-/kloc-0.

For the same exposure, you can find various apertures and shutter speeds (exposure pairs)-more than ten kinds. Close observation of photos: If the image is blurred, blurred and the subject is blurred, it means that the shutter speed used by the exposure camera is too slow.

Sensitivity (ISO)

Photosensitivity indicates the sensitivity of the substrate to the incident luminous flux. ISO value can be two photocells: film or sensor. It means that one of the elements can perceive light. The higher the ISO value, the brighter the photo.

The numerical value may vary greatly, and it will be different for different lenses, and it will be combined with other parameters in different ways. For high sensitivity (ISO greater than 400), use short exposure time; For low values as low as ISO 100, use fast shutter speed and constant aperture value.

Usually, if the sensitivity is large, there will be too much digital noise when shooting on a digital camera, similar to film particles. Sometimes, the correct color reproduction may even be reduced or lost-that's why you should try to choose the correct ISO that won't destroy the picture.

3. How do the exposure parameters interact?

Exposure assumes that a certain amount of light shines on the sensor. The bigger the image, the brighter it is, and the smaller it is, the darker it is. The three parameters mentioned above (aperture size, shutter speed and ISO sensitivity) are closely related: change one and you will automatically change the other two parameters. It is worth giving an example that all the elements are so closely related.

For example, if the shooting position is well lit and then the aperture is turned on, we will transfer a lot of light to the matrix. Lowering the shutter speed and setting the minimum ISO sensitivity will help to take photos without overexposure.

When the light is obviously not enough to take a successful photo, an aperture opening is never enough to make the exposure satisfactory and good. This means that it is worthwhile to increase the exposure-after all, there are not enough beams entering the matrix, which means that it will take more time to properly expose. And according to the result to be achieved, the photosensitivity has been improved to a certain expected value.

These two kinds of interactions are classic cases, which are helpful to understand the structural principle.

Exposure control mode

Modern digital cameras and SLR cameras provide us with the choice of exposure methods. * * * There are three options for how to use aperture, shutter speed and ISO:

Manual mode (indicated by the letter m). We can independently adjust all three parameters we need: aperture value, shutter speed and ISO sensitivity;

Aperture priority mode (identified by Av or A). Here, parameters such as aperture and sensitivity can be controlled independently, but the camera will automatically control the shutter speed.

Shutter priority mode (indicated by Tv or S). Here, the camera has already controlled the aperture value. However, the ISO value and shutter speed can be used independently.

Fourth, exposure compensation.

Now it is known that in addition to the most important and important exposure parameters such as aperture, shutter speed and sensitivity, another parameter-exposure compensation can be added to the group.

Then apply exposure compensation, set the box, all the basic parameters have been set, and the camera has measured the exposure. Exposure compensation allows you to slightly correct the image to make it darker or brighter. For this mode, each manufacturer even assigned a separate button to the camera.

If you correct it, you will find that the exposure has changed by about 0.3 units, which can be changed through the menu on the camera. Exposure compensation can be used to correct the brightness of photos in the shortest time.

Now every novice photographer will understand the importance of using exposure and its exposure parameters. There are countless subtle differences in photography, and even photography professionals have been exploring ways, which is why we should consider the fact that we need to practice photography frequently.