What factors will affect the exposure?

Lead: In the case of overexposure, the negative will appear too dark and the developed photos will turn white. In the case of insufficient development and excessive aperture during development, the color of the photo will also turn white. Sometimes it is also caused by the too strong light of the flash.

What factors will affect the exposure? Next, let's take a look at the first lesson of photography for beginners.

As we know, exposure is determined by aperture, shutter and ISO speed. Having said that, some beginners may be confused. Let's answer your questions.

The control of exposure is determined by aperture value, shutter speed and ISO sensitivity. Then we will explain to you in principle how the changes of various variables will affect the exposure.

The aperture control structure of a lens usually consists of a plurality of aperture blades. With the opening or contraction of the diaphragm blades, the amount of light passing through the diaphragm is controlled. When the opening area of the aperture blade is large, a lot of light will pass through the aperture at the same time; When the aperture is reduced to a very small value, only a small amount of light passes through at the same time.

The aperture value is determined by the aperture value. Aperture value is a unitless dimension, which generally consists of capital letter f plus numbers. The smaller the number after the letter f, the larger the aperture value; The larger the number after the letter, the smaller the aperture value. What is the aperture value? Shielding Let's measure, the ratio of aperture values of adjacent gears is 1.4. For example, the aperture value of F2.8 is larger than that of F4 1 step. So what does 1 aperture mean? It means that in the same time, the amount of light passing through the aperture with an aperture value of F2.8 is twice that of F4. Reflected in the aperture area of the aperture blade, the aperture area of the aperture blade is twice the aperture value of F4 when the aperture value is F2.8.

After the aperture value, let's talk about the shutter speed. The shutter speed directly controls the exposure time. Shutter control mechanism will have a curtain with shading effect to block the photosensitive element. When we completely press the shutter button, the shutter curtain opens and the photosensitive element is photosensitive; After the exposure, close the shutter curtain. Shutter speed is generally in seconds. The higher the shutter speed, the less light reaches the photosensitive element through the shutter system. The lower the shutter speed, the greater the amount of light passing through the shutter system.

There is also a control variable to control the exposure, which is the sensitivity of the photosensitive element. Sensitivity is a measure of the sensitivity of photosensitive elements to light. In digital SLR cameras in the film age, the sensitivity is determined by the film used by photographers. Once a photographer has installed a film with a specific sensitivity, if he wants to change the sensitivity, he can only change it to a film with other sensitivity. In the digital age, it is very easy to change the sensitivity, just set it in the camera. The unit of sensitivity is ISO, and the sensitivity with high ISO value is more sensitive to light than the sensitivity with low ISO value. That is to say, after the same amount of light reaches the photosensitive element, the photosensitive element can capture more light by using the sensitivity with high ISO value.

Wouldn't it be better if we used high ISO sensitivity? Sensitivity is a double-edged sword. Increasing the ISO value will make the photosensitive element more sensitive to light, but it will also produce more noise on the screen. The photos taken with low ISO value have pure pictures and bright details. When we improve the sensitivity, there is obvious noise on the picture, and the details of the picture will be seriously lost.

Aperture, shutter speed and ISO sensitivity all affect exposure.

Above we introduced the aperture, shutter speed and ISO sensitivity, which will affect the exposure. Next, we will introduce how these three variables * * * affect the exposure.

We mentioned above that the aperture value will affect the exposure. Then when we shoot with a larger aperture value, more light will pass through the aperture control mechanism at the same time. If we increase the aperture by one step, we will increase the exposure by one step on the premise that the shutter speed and ISO sensitivity remain unchanged. Reflected in the photo, the picture will be brighter, and vice versa.

When we set a faster shutter speed, it means a shorter exposure time. Under the premise of constant aperture and ISO sensitivity, shorter exposure time will reduce exposure and the picture of the photo will be darker. If you use a slower shutter speed, the exposure time will be longer and the picture will be brighter.

After talking about aperture value and shutter speed, let's take a look at ISO sensitivity. As mentioned above, high ISO sensitivity is more sensitive to light. When the same amount of light reaches the photosensitive element, the photosensitive element will capture more light when using high ISO value. When the aperture and shutter speed are inconvenient, the exposure will increase by 1 times for every ISO increase in sensitivity.

Two of the three variables, aperture, shutter speed and ISO sensitivity, remain unchanged, and the other variable changes the influence on exposure. So what if two or three of these three variables change? I believe this is the difficulty of exposure control. Here is a common rule of exposure control. The law of reciprocity.

Let's take an example first: which exposure is larger, aperture F2.8, shutter speed 1/500 seconds, F4+000, or ISO65438, shutter speed 1/250 seconds, ISO 100? The answer is that the combination of these two exposure parameters produces the same exposure. As can be seen from this example, the exposure is the same when the aperture is reduced by one step and the shutter speed is reduced by one step, and the sensitivity is unchanged.

When more than two variables change, it is only necessary to synthesize the influence of the change amount of each variable on the exposure. For example, if the shutter speed increases by one gear, the exposure will decrease by one gear; At the same time, the aperture is opened by one gear, and the exposure will increase by one gear; Double ISO sensitivity and increase exposure by one level. On the whole, the change of aperture value and ISO sensitivity will increase two exposures, and the change of shutter speed will decrease one exposure. After the positive and negative cancellation, the exposure actually increased by a step.

The influencing factors of exposure and how the changes of these influencing factors will affect exposure are the difficulties in exposure control. I hope the above knowledge can help you understand the exposure control.