Calculation formula of aperture

Aperture f value = lens focal length/lens aperture diameter

As can be seen from the above formula, to achieve the same aperture f value, the aperture of a long focal length lens is larger than that of a short focal length lens.

The complete series of aperture values are as follows: F 1.0, F 1.4, F2.0, F2.8, F4.0, F5.6, F8.0, F1,F 16, F2.

The gear design of the aperture is that the numerical difference between two adjacent gears is 1.4 times (the square root of 2 is the approximate value of 1.4 14), the diameter of the light-transmitting hole is twice the root number, the area of the light-transmitting hole is twice different, the brightness of imaging on the negative is twice different, and the time required to keep the same exposure is twice different.

It is worth mentioning that the smaller the f value of the aperture, the larger the aperture (as shown in the right figure), and the more light enters in the same unit time, and the light entering the upper level is exactly twice that of the lower level. For example, if the aperture is adjusted from F8 to F5.6, the amount of light entering will double. We also say that the aperture is enlarged by one level. The luminous flux of F5.6 is twice that of F8. Similarly, F2 is 16 times the luminous flux of F8. When F8 is adjusted to F2, the aperture is enlarged by four levels. For consumer digital cameras, the aperture f value is often between F2.8-F 1 1. In addition, many digital cameras can adjust the aperture by 1/3.

The function of the aperture is to determine the amount of light entering the lens. The smaller the value after f, the larger the aperture and the more light entering. On the contrary, the smaller. Simply put, under the condition that the shutter speed (exposure speed) is constant, the smaller the aperture f value, the larger the aperture, and the more light enters, the brighter the picture; The larger the aperture f value, the smaller the aperture and the darker the picture.

Aperture and shutter take precedence.

In addition to providing automatic mode, high-end digital cameras usually have two options: aperture priority and shutter priority, so that you can decide a certain aperture value or a certain shutter value on some occasions, and then match the appropriate shutter or aperture respectively to present different depth of field (sharpness) or effects.

Aperture priority mode

After we decide the aperture f value ourselves, the camera metering system will automatically choose the appropriate shutter speed (which can be an accurate stepless shutter speed) according to the light conditions at that time. A digital camera with an exposure mode dial usually engraves an "A" on the dial to indicate the aperture priority mode. Aperture priority mode is suitable for photography that emphasizes the depth of field effect.

Because the focal length of digital camera is much shorter than that of traditional camera and the aperture of lens is small, it is difficult to produce narrow depth of field. Some digital cameras have a special portrait exposure mode, which uses built-in programs and a large aperture to blur the foreground and background.