How is the aperture gear set?

Aperture is a geometric series, and the median is actually the common ratio, and the common ratio multiplied by the above value is the median. The usual aperture value takes two significant figures, followed by decimal truncation. The common ratio of the whole aperture is the root number 2, 1.4438+042. The common ratio of half aperture is 24, 1. 1892. The aperture ratio of 1/3 gear is 2 to the 6th power, 1.5438+0225.

Aperture = focal length ÷ entrance aperture of the lens. For example, for a 50mm fixed-focus lens, when the aperture is F4, the incident aperture of the lens = 50 mm ÷ 4 =12.5 mm; When the aperture becomes F2, the entrance aperture of the lens = 50 mm ÷ 2 = 25 mm ..

Therefore, the smaller the aperture value, such as F2, the larger the entrance aperture, which is called large aperture; Conversely, the larger the aperture, such as F22, the smaller the entrance aperture, which is called small aperture.

Extended data

Common aperture gear

As a parameter for controlling exposure, the aperture is divided into multiple gears. As shown below, 2, 2.8, 4, 5.6, 8, 1 1, 16, 22, etc. It is the aperture series that we need to remember.

The exposure relationship between adjacent gears is x2, and the common gears of aperture are also easy to remember:

2、2.8;

4、5.6;

8、 1 1;

16、22;

The values of two columns of vertical shots are equal to twice that of the previous row, such as 16=8x2, 8=4x2, and 4=2x2. It can be concluded that F 1.4 and F 1.2 precede F2, while F32, F44 and F64 follow F22. But the common aperture values are 1.2, 1.42, 2.8, 4, 5.6, 8, 1 1,16,22.