How to determine the effective aperture of camera aperture?

The ratio of the incident aperture to the focal length of the objective lens is called the relative aperture of the photographic objective lens, which is an important factor to determine the transmittance and resolution of the objective lens. It is generally expressed by its reciprocal form f, which is called the aperture number. For example, f4 indicates that the focal length of the objective lens is four times the diameter of the incident aperture.

The standard of relative aperture of objective lens is generally 1, 1.4, 2, 2.8, 4, 5.6, 8, 1 1, 22, 32. The ratio of two adjacent gears is root number 2.

Photographic objective lens can be divided into:

Ultra-transparent objective lens 1:2.8 or above.

Strong light transmission objective 1:3.5~ 1:5.8

Normal transmission objective 1:6.3~ 1:9

The weak light transmission objective lens is less than 1:9.